tag:theconversation.com,2011:/au/topics/smells-15316/articlesSmells – The Conversation2024-02-09T16:50:23Ztag:theconversation.com,2011:article/2153112024-02-09T16:50:23Z2024-02-09T16:50:23ZYour unique smell can provide clues about how healthy you are<figure><img src="https://images.theconversation.com/files/574043/original/file-20240207-19-o4ehc8.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5291%2C3516&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/happy-calm-teen-girl-enjoying-good-1325627765">fizkes/Shutterstock</a></span></figcaption></figure><p>Hundreds of chemicals stream from our bodies into the air every second. These chemicals release into the air easily as they have high vapour pressures, meaning they boil and turn into gases at room temperature. They give clues about who we are, and how healthy we are. </p>
<p>Since ancient Greek times, we’ve known that we smell differently when we are unwell. While we rely on blood analysis today, ancient Greek physicians used smell to diagnose maladies. If they took a whiff of your breath and described it as <em>fetor hepaticus</em> (meaning bad liver), it meant you could be headed for liver failure.</p>
<p>If a person’s whiff was sweet or fruity, physicians thought this meant that sugars in the digestive system were not being broken down, and that person had probably diabetes. Science has since shown the ancient Greeks were right – liver failure and <a href="https://tisserandinstitute.org/human-volatilome/">diabetes</a> and many <a href="https://link.springer.com/article/10.1007/s00216-023-04986-z">other diseases</a> including infectious diseases give your breath a distinctive smell.</p>
<p>In 1971, <a href="https://www.nobelprize.org/prizes/peace/1962/pauling/facts/">Nobel Laureate chemist Linus Pauling</a> <a href="https://edu.rsc.org/feature/breath-analysis/2020106.article#:%7E:text=The%20'modern%20era'%20of%20breath,in%20an%20average%20breath%20sample.">counted 250 different</a> gaseous chemicals in breath. These gaseous chemicals are called volatile organic compounds or VOCs. </p>
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<p>Since Pauling’s discovery, other scientists have <a href="https://link.springer.com/article/10.1007/s40291-023-00640-7">discovered hundreds more VOCs</a> in our breath. We have learned that many of these VOCs have distinctive odours, but some have no odour that our noses can perceive. </p>
<p>Scientists believe that whether a VOC <a href="https://tisserandinstitute.org/human-volatilome/">has an odour</a> that our noses can detect or not, they can reveal information about how healthy someone is.</p>
<p>A Scottish man’s Parkinson’s disease onset was <a href="https://www.bbc.co.uk/news/uk-scotland-47627179">identified by his wife</a>, retired nurse Joy Milner, after she was convinced the way he smelled had changed, years before he was diagnosed in 2005. This discovery has <a href="https://www.manchester.ac.uk/discover/news/smell-of-skin-could-lead-to-early-diagnosis-for-parkinsons/">led to research programmes</a> involving Joy Milner to identify <a href="https://www.scientificamerican.com/article/a-supersmeller-can-detect-the-scent-of-parkinsons-leading-to-an-experimental-test-for-the-illness/">the precise smell</a> of this disease. </p>
<p>Dogs can <a href="https://www.nature.com/articles/d41586-022-01629-8">sniff out more diseases</a> than humans because of their more <a href="https://www.understandinganimalresearch.org.uk/news/the-science-of-sniffs-disease-smelling-dogs%20-%20I%20think%20the%20previous%20nature%20link%20has%20more%20credibility%20for%20here%20also">sophisticated olfactory talents</a>. But technological techniques, like <a href="https://www.britannica.com/science/mass-spectrometry">analytical tool mass spectrometry</a>, picks up even more subtle changes in VOC profiles that are being linked to <a href="https://www.thelancet.com/journals/ebiom/article/PIIS2352-3964(20)30100-6/fulltext">gut</a>, <a href="https://www-sciencedirect-com.dcu.idm.oclc.org/science/article/pii/S0165993618305168">skin</a> and <a href="https://err.ersjournals.com/content/28/152/190011">respiratory</a> diseases as well as neurological diseases like Parkinson’s. Researchers believe that one day some diseases will be diagnosed simply by breathing into a device. </p>
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<h2>Where do VOCs come from?</h2>
<p>Breath is not the only source of VOCs in the body. They are also emitted from skin, urine and faeces. </p>
<p>VOCs from skin are the result of millions of skin glands removing metabolic waste from the body, as well as waste generated by bacteria and other microbes that live on our skin. Sweating produces extra nutrients for these bacteria to metabolise which can result in particularly odorous VOCs. Odour from sweat only makes up a fraction of the scents from VOCs though.</p>
<p><a href="https://www.nature.com/articles/nrmicro.2017.157">Our skin</a> and also our gut microbiomes are made up from a delicate balance of these microbes. Scientists think <a href="https://journals.lww.com/co-gastroenterology/abstract/2015/01000/the_gut_microbiome_in_health_and_in_disease.12.aspx">they influence our health</a>, but we don’t yet understand a lot about how this relationship works. </p>
<p>Unlike the gut, the skin is relatively easy to study – you can collect skin samples from living humans without having to go deep into the body. <a href="https://www-sciencedirect-com.dcu.idm.oclc.org/science/article/pii/S1471492221002087">Scientists think</a> skin VOCs can offer insights into how the microbiome’s bacteria and the human body work together to maintain our health and protect us from disease.</p>
<p>In my team’s laboratory, <a href="https://iopscience.iop.org/article/10.1088/1752-7163/abf20a">we are investigating</a> whether the skin VOC signature can reveal different attributes of the person it belongs to. These signals in skin VOC signatures are probably how dogs distinguish between people by smell. </p>
<p>We are at a relatively early stage in this research area but we have shown that you can tell males from females based on how acidic the VOCs from skin are. We use mass spectrometry to see this as the average human nose is not sophisticated enough to detect these VOCs. </p>
<p>We can also predict a person’s age with reasonable accuracy to within a few years from their skin VOC profile. This is not surprising considering that oxidative stress in our bodies increases as we age.</p>
<p><a href="https://www.metabolismjournal.com/article/S0026-0495(00)80077-3/pdf">Oxidative stress</a> happens when your antioxidant levels are low and causes irreversible damage to our cells and organs. <a href="https://pubs.acs.org/doi/10.1021/jasms.3c00315">Our recent research</a> found by-products of this oxidative damage in skin VOC profiles. </p>
<p>Not only are these VOCs responsible for personal scent – they are used by plants, insects and animals as a communication channel. Plants are in a <a href="https://www.nature.com/articles/s41598-017-10975-x">constant VOC dialogue</a> with other organisms including pollinators, herbivores, other plants and their natural enemies such as harmful bacteria and insects. VOCs used for this back and forth dialogue are known as pheromones. </p>
<h2>What has science shown about love pheromones?</h2>
<p>In the animal kingdom, there is good evidence VOCs can act as aphrodisiacs. Mice for example have microbes which contribute to a particularly <a href="https://www.sciencedirect.com/science/article/pii/S0960982212012687">smelly compound called trimethylamine</a>, which allows mice to verify the species of a potential mate. <a href="https://www.sciencedirect.com/science/article/abs/pii/S0093691X21003083">Pigs</a> and <a href="https://www.nature.com/articles/4381097a">elephants</a> have sex pheromones too. </p>
<p>It is possible that humans also produce VOCs for attracting the perfect mate. Scientists have yet to fully decode skin – or other VOCs that are released from our bodies. But evidence for human love pheromones so far is <a href="https://www.science.org/content/article/do-human-pheromones-actually-exist">controversial at best</a>. <a href="https://www.newscientist.com/article/dn3835-colour-vision-ended-human-pheromone-use/">One theory suggests</a> that they were lost about 23 million years ago when primates developed full colour vision and started relying on their enhanced vision to choose a mate.</p>
<p>However, we believe that whether human pheromones exist or not, skin VOCs can reveal who and how we are, in terms of things like ageing, nutrition and fitness, fertility and even stress levels. This signature probably contains markers we can use to monitor our health and diagnose disease.</p><img src="https://counter.theconversation.com/content/215311/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aoife Morrin receives funding from Science Foundation Ireland.</span></em></p>The science of smell is an exciting area of research.Aoife Morrin, Associate Professor of Analytical Chemistry, Dublin City UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2126442023-09-27T13:40:03Z2023-09-27T13:40:03ZThe tantalising scent of rain or freshly baked bread: why can certain smells transport us back in time?<figure><img src="https://images.theconversation.com/files/545770/original/file-20230817-27-s2icj0.jpg?ixlib=rb-1.1.0&rect=0%2C22%2C7348%2C4880&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/es/image-photo/selective-focus-cheerful-asian-woman-smiling-1460132408">LightField Studios / Shutterstock</a></span></figcaption></figure><p>My father was a carpenter, meaning I have spent a great deal of my life surrounded by wood, saws, planes and chisels. Simply by living among sawdust and woodchips, you learn to distinguish the different smells of wood.</p>
<p>Years after my father retired, I was walking through the underbelly of a hospital when, completely by chance, I stumbled upon the maintenance room. The smell of that room enveloped me, travelling instantaneously through my olfactory mucosa, to the olfactory nerve and then the olfactory bulb which, after a swift analysis, directed it to my limbic system. </p>
<p>Suddenly and unexpectedly, I was transported back to my native Toledo (in Spain), to my father’s carpentry workshop. It had been closed for years and I had never given it much thought, but for a second I felt I could see him in front of me, sanding block in hand, beckoning me over to help. And as if by magic, all the stress of my day began to evaporate, giving way to a serene sense of calm and happiness.</p>
<p>The noise of a nearby elevator snapped me back to reality.</p>
<h2>Smells that revive past emotions</h2>
<p>Is it possible that the mere smell of freshly cut wood had transported me back 20 years, and that my hippocampus was dredging up memories that I did not even know were there?</p>
<p>These kinds of occurrences are very common, as, undoubtedly, you can confirm. The scent of freshly baked cakes or bread, the chlorine of a swimming pool in summer, a salty sea breeze, coffee, and rain are smells that cause our minds to recover memories and emotions that we thought long forgotten.</p>
<p>Memory is the brain’s ability to compile, store and recover information based on past experiences. But what kinds of experiences are most easily stored? It is those connected to <a href="https://theconversation.com/tiene-nuestro-cerebro-un-boton-para-borrar-los-malos-recuerdos-194854">emotion</a>, whether positive or negative.</p>
<p>Our memories are like a bottomless drawer. The amount of information they can store is infinite, but it is not always easy to access. This is because our brains tuck away things that they consider to be less important at any given moment. The more hidden a piece of information is, the more difficult it is to retrieve.</p>
<p>Numerous scientific studies have tried to discover how we can recover memories and sensations from the past through a particular smell. This is known as <a href="https://www.sciencedirect.com/topics/neuroscience/olfactory-memory">olfactory memory</a>.</p>
<h2>A direct line to emotional memory</h2>
<p>The sense of smell is strongly connected to different areas of the brain, such as the limbic system and the orbitofrontal cortex. The former is essential in creating emotional responses to smells, while the latter helps to identify and distinguish them, as well as linking them to specific experiences and memories.</p>
<p>Before it reaches the cerebral cortex, information from the other senses must first pass through a control system, the thalamus. The sense of smell, however, has a VIP pass, and it bypasses the thalamus to connect directly to the brain’s memory circuits, located in the hippocampus.</p>
<p>For this reason, a familiar smell activates the same areas of the brain as those related to emotional memory. In fact, scent induced memories tend to be connected to past experiences with a greater emotional significance than other senses.</p>
<h2>The loss of smell, a sign of neurological illness</h2>
<p>Much like other senses, our sense of smell seems to diminish as we get older, but it can also be linked to various disorders. Many of us experienced this first hand <a href="https://pubmed.ncbi.nlm.nih.gov/32563019/">during the covid-19 pandemic</a>, when millions of people lost their sense of smell. For most this was temporary, but for some it was permanent.</p>
<p>Intriguingly, many disorders linked to a loss of smell are neurodegenerative, where one of the associated symptoms is memory loss.</p>
<p>It is significant that this deterioration of smell may precede other problems, as it can therefore be used to predict almost 70 <a href="https://pubmed.ncbi.nlm.nih.gov/30083097/">psychiatric and neurological conditions</a>. Continued decline in the ability to detect odours heralds the loss of grey matter – mostly made up of neurons – in the hippocampus as <a href="https://pubmed.ncbi.nlm.nih.gov/34893841">mild cognitive impairment (MCI)</a> sets in, and then subsequently progresses to <a href="https://pubmed.ncbi.nlm.nih.gov/26696886/">Alzheimer’s disease</a>.</p>
<p>In fact, a declining sense of smell can <a href="https://academic.oup.com/acn/article/28/5/391/5707?login=false">predict</a> whether individuals with MCI will develop Alzheimer’s in the future. But this does not just help to detect dementia: it can also be a sign of <a href="https://pubmed.ncbi.nlm.nih.gov/29360225/">cognitive dysfunction</a> and precedes or develops alongside a wide range of conditions such as <a href="https://pubmed.ncbi.nlm.nih.gov/20858529/">Parkinson’s disease</a>, <a href="https://pubmed.ncbi.nlm.nih.gov/16991138/">Lewy body dementia</a>, <a href="https://pubmed.ncbi.nlm.nih.gov/14755736/">Creutzfeldt-Jakob disease</a>, <a href="https://pubmed.ncbi.nlm.nih.gov/12658108/">alcoholism</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/20825265/">schizophrenia</a>. </p>
<h2>Olfactory gymnastics to rehabilitate your memory?</h2>
<p>In the case of people suffering from neurological conditions such as Alzheimer’s or Parkinson’s, the absence of olfactory stimulation in the brain can actually cause other symptoms to worsen. In fact, <a href="https://www.frontiersin.org/articles/10.3389/fnins.2020.00140/full">several studies</a> have drawn a connection between a strong sense of smell and a lower overall risk of mortality.</p>
<p>Consequently, in recent years there has been interest in determining the therapeutic potential of scents to stimulate and rehabilitate memory in patients with neurological disorders.</p>
<p>Information available to date suggests that there is a connection. Olfactory enrichment –smelling a range of different scents– can reverse loss of smell caused by an <a href="https://pubmed.ncbi.nlm.nih.gov/27017331/">infection</a>, <a href="https://pubmed.ncbi.nlm.nih.gov/33486898/">craneal trauma</a>, <a href="https://pubmed.ncbi.nlm.nih.gov/23613901/">Parkinson’s</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/34867284/">aging</a>. This improvement is associated with an increase in cognitive and memory capacity.</p>
<p>The method for this form of therapy could not be simpler: results are achieved by exposing people daily to various scents. A recent study supports the idea that two hours per night, over six months, is enough to improve memory function.</p>
<p>Obviously, more research is needed to definitively conclude that regular olfactory stimulation helps to protect the brain and prevent cognitive decline or impairment.</p>
<p>Until this happens, I will return to my father’s carpentry shop, thinking of these words by Marcel Proust: “Perfume is that last and best reserve of the past, the one which when all out tears have run dry, can make us cry again.”</p><img src="https://counter.theconversation.com/content/212644/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>José A. Morales García no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.</span></em></p>The sense of smell is directly connected to areas of the brain linked to memory and emotions. That is why some smells bring to light memories and feelings we thought we had forgotten.José A. Morales García, Investigador científico en enfermedades neurodegenerativas y Profesor de la Facultad de Medicina, Universidad Complutense de MadridLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1833632022-05-20T00:41:00Z2022-05-20T00:41:00ZCan sniffer dogs really detect COVID almost as well as a PCR test? Turns out they can<figure><img src="https://images.theconversation.com/files/464382/original/file-20220519-26-gkluh1.jpg?ixlib=rb-1.1.0&rect=2%2C2%2C1914%2C1273&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/N04FIfHhv_k">Victor Grabarczyk/unsplash</a></span></figcaption></figure><p>Dogs have an exceptional sense of smell. We take advantage of this ability in many ways, including by training them to find illicit drugs, dangerous goods and even people. </p>
<p>In recent years, a dog’s sense of smell has also been used in the medical field. These remarkable animals can be trained to <a href="https://theconversation.com/the-scent-of-sickness-5-questions-answered-about-using-dogs-and-mice-and-ferrets-to-detect-disease-151832">sniff out</a> cancer, diabetes, and extraordinarily, <a href="https://www.nature.com/articles/s41598-019-40721-4">epileptic seizures</a> before they occur.</p>
<p>Early in the pandemic the possibility of using dogs to sniff out COVID was explored in a few countries. And although the results of these early trials surpassed most people’s expectations, many <a href="https://theconversation.com/yes-dogs-can-sniff-out-covid-but-not-after-dinner-when-they-need-a-nap-161669">questions remained</a>. These included how well these findings would stand up to more rigorous scientific scrutiny and how well dogs would perform outside the artificial environment of the research laboratory.</p>
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<a href="https://theconversation.com/yes-dogs-can-sniff-out-covid-but-not-after-dinner-when-they-need-a-nap-161669">Yes, dogs can sniff out COVID. But not after dinner, when they need a nap</a>
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<p>In the past week we have moved closer to answering these questions, with an article published in <a href="https://gh.bmj.com/content/7/5/e008024">BMJ Global Health</a>, which found dogs could detect COVID almost as well as PCR tests, in some circumstances.</p>
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<h2>What did the researchers test?</h2>
<p>This article reported the results of two studies. In both studies, four dogs were tested to see how well they detected COVID from skin swabs taken from people with or without COVID (according to the gold-standard test, PCR). </p>
<p>These dogs didn’t just come off the streets; they had already had a significant amount of training in sniffing out drugs, dangerous goods or cancer.</p>
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Read more:
<a href="https://theconversation.com/the-scent-of-sickness-5-questions-answered-about-using-dogs-and-mice-and-ferrets-to-detect-disease-151832">The scent of sickness: 5 questions answered about using dogs – and mice and ferrets – to detect disease</a>
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<h2>The first study</h2>
<p>In the first study, the researchers looked at whether the dogs could identify COVID in the skin swabs of 420 volunteers, 114 of whom had tested positive to COVID by PCR. </p>
<p>The study was rigorous, with various precautions against the results being compromised. This included an elaborate study protocol that involved a number of separate assistants and a dog handler. None of them knew whether the sample was from someone with COVID, so they could not influence the outcome, intentionally or unintentionally.</p>
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<span class="caption">Neither the dog handler or assistants knew who had COVID and who didn’t.</span>
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<p>The dogs detected COVID with a sensitivity of 92% (which refers to their ability to correctly identify those with infection) and a specificity of 91% (their ability to correctly identify those without infection). </p>
<p>Although there was some variation between dogs, they all performed exceptionally well. There are no significant disclaimers here, this was a great result.</p>
<h2>The second study</h2>
<p>The second study was important as its goal was to see how well the dogs could do in the messiness of the real world. This real-life trial involved the dogs sniffing 303 incoming passengers at Helsinki-Vantaa International Airport in Finland. Each passenger also took a PCR test. </p>
<p>The dogs matched the PCR results in 296 out of 303 (98%) of the samples and they correctly identified the swabs as negative in 296 out of 300 (99%) samples.</p>
<p>The important consideration in interpreting this result is this happened during airport screening, a situation where you wouldn’t expect many people to test positive.</p>
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<span class="caption">Sometimes tired doggies just need a bit of a lie down.</span>
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<p>In this type of low-prevalence environment, you want dogs to be able to screen passengers with a high “negative predictive value”. That is, you want the dogs to be able to identify people who are not carrying the virus to differentiate them from those who may be carrying it. Then you would carry out confirmatory PCR testing on that last group.</p>
<p>In an environment where the prevalence of COVID is around 1%, such as an airport, the researchers estimated the “negative predictive value” for dogs screening for COVID to be 99.9%. That is, the dogs would be expected to correctly exclude 99.9% of passengers as having COVID. This is another fantastic result.</p>
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Read more:
<a href="https://theconversation.com/want-to-cut-your-chance-of-catching-covid-on-a-plane-wear-a-mask-and-avoid-business-class-180333">Want to cut your chance of catching COVID on a plane? Wear a mask and avoid business class</a>
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<h2>Low tech and instant</h2>
<p>In a world where we rely on expensive technological solutions, there is something reassuring about finding a low-tech option for screening COVID. </p>
<p>Importantly, however, the study highlights dogs are quick to train for this task and are ideal for screening in high-throughput settings, such as airports, given how accurate they are and the fact they give instant results.</p>
<p>Although nothing should surprise us about our closest friend, another incredible outcome from this study was the suggestion the dogs may have been able to distinguish between the variants of SARS-CoV-2, the virus that causes COVID. </p>
<p>While other possible explanations cannot be excluded, the performance of the dogs seemed to drop with the emergence of the Alpha variant. This was attributed to the dogs being able to identify a difference between this variant and the wild-type virus on which they were originally trained. </p>
<p>These studies confirm nothing could be further from the truth when we say you can’t teach an old dog new tricks.</p>
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Read more:
<a href="https://theconversation.com/why-are-there-so-many-new-omicron-sub-variants-like-ba-4-and-ba-5-will-i-be-reinfected-is-the-virus-mutating-faster-182274">Why are there so many new Omicron sub-variants, like BA.4 and BA.5? Will I be reinfected? Is the virus mutating faster?</a>
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<img src="https://counter.theconversation.com/content/183363/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hassan Vally does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>With the right training, dogs can sniff out more than 90% of COVID cases.Hassan Vally, Associate Professor, Epidemiology, Deakin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1652162021-08-05T11:09:12Z2021-08-05T11:09:12ZHow we created fake smells to trick predators and save endangered birds – podcast<figure><img src="https://images.theconversation.com/files/413565/original/file-20210728-19-1rl37m6.jpg?ixlib=rb-1.1.0&rect=101%2C15%2C2393%2C1696&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">‘Fake news’ odours are protecting vulnerable birds and their offspring, including the banded dotterel. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/double-banded-dotterel-australasia-1420141502">Imogen Warren/Shutterstock</a></span></figcaption></figure><p><em>The Conversation Weekly podcast is taking a short break in August. For the next few weeks we’ll be bringing you extended versions of some our favourite interviews from the past few months.</em></p>
<p>This week, the story of researchers who invented an ingenious new conservation technique to protect endangered birds. </p>
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<p>In many places, bird populations are plummeting, in part due to hungry and often invasive predators. This isn’t an easy problem to solve for conservation biologists. Either you need to kill the predators – which is really hard and comes with its own ethical questions – or you need to build protection for the birds’ nests which can damage the environment. </p>
<p>Catherine Price, postdoctoral researcher in conservation biology at the University of Sydney, is part of a team of researchers who’ve found a better way. They used misinformation – in the form of fake smells – to fool predators into leaving bird nests alone. She told us how the concept works, and what she and her colleagues found when they tested it out in the Mackenzie Basin on New Zealand’s South Island. </p>
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<strong>
Read more:
<a href="https://theconversation.com/scientists-used-fake-news-to-stop-predators-killing-endangered-birds-and-the-result-was-remarkable-152320">Scientists used 'fake news' to stop predators killing endangered birds — and the result was remarkable</a>
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<p>This episode of The Conversation Weekly features an extended version of an interview <a href="https://theconversation.com/the-zombie-company-problem-and-what-it-means-for-our-economies-podcast-158544">first published on April 9</a>. The episode was produced by Mend Mariwany and Gemma Ware, with sound design by Eloise Stevens. Our theme music is by Neeta Sarl. You can find us on Twitter <a href="https://twitter.com/TC_Audio">@TC_Audio</a>, on Instagram at <a href="https://www.instagram.com/theconversationdotcom/?hl=en">theconversationdotcom</a>. or via email on podcast@theconversation.com. You can also sign up to <a href="https://theconversation.com/newsletter?utm_campaign=PodcastTCWeekly&utm_content=newsletter&utm_source=podcast">The Conversation’s free daily email here</a>.</p>
<p><em>You can listen to The Conversation Weekly via any of the apps listed above, download it directly via our <a href="https://feeds.acast.com/public/shows/60087127b9687759d637bade">RSS feed</a>, or find out how else to <a href="https://theconversation.com/how-to-listen-to-the-conversations-podcasts-154131">listen here</a>.</em></p><img src="https://counter.theconversation.com/content/165216/count.gif" alt="The Conversation" width="1" height="1" />
From the archive: using misinformation to fool predators into leaving bird nests alone. Listen to The Conversation Weekly podcast.Gemma Ware, Head of AudioDaniel Merino, Associate Breaking News Editor and Co-Host of The Conversation Weekly PodcastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1585442021-04-08T10:28:07Z2021-04-08T10:28:07ZThe zombie company problem and what it means for our economies – podcast<figure><img src="https://images.theconversation.com/files/393817/original/file-20210407-13-ln22uq.jpg?ixlib=rb-1.1.0&rect=125%2C71%2C5784%2C3700&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Beware of zombie companies. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/zombie-walking-out-abandoned-city-silhouettes-462287122">solar22 via Shutterstock</a></span></figcaption></figure><p>In this episode of <a href="https://theconversation.com/uk/topics/the-conversation-weekly-98901">The Conversation Weekly</a>, why some economists are worried about a growing army of “zombie companies” with lots of debts – and what this could mean for the shape of our economies. And researchers have found a new way to prevent predators from eating endangered birds and their eggs – via a form of biological, psychological warfare. </p>
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<p><iframe id="tc-infographic-561" class="tc-infographic" height="100" src="https://cdn.theconversation.com/infographics/561/4fbbd099d631750693d02bac632430b71b37cd5f/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>With interest rates at record lows, many companies have been able to borrow money at very little cost. This cheap cash, which was flooding financial markets before the pandemic began, led some companies to rack up some big debts. Economists call these <a href="https://theconversation.com/attack-of-zombie-companies-dont-let-them-eat-bailouts-that-are-vital-to-restore-the-economy-139177">“zombie companies”</a> – firms that may struggle to pay the interest on their large debts. It’s a problem that’s been exacerbated by the pandemic, as revenues dried up in many sectors of the economy. </p>
<p>Governments around the world have stepped in to help companies through the economic crisis caused by COVID-19, but there may be a reckoning ahead. Karl Schmedders, professor of finance at the International Institute for Management Development in Lausanne, Switzerland, explains how zombie companies are born and why the pandemic could have made the problem worse. “It will be a very difficult process to slow down the support of worldwide economies without causing another recession that then is caused by zombie company insolvencies,” he tells us. Schmedders says 2021 is likely to see a wave of mergers and acquisitions as a result. </p>
<p>We also hear from Sandy Brian Hager, senior lecturer in international political economy at City, University of London, about why the size of a company has a bearing on how easy it’s been able to access all this cheap money. His research shows that smaller US corporations have been <a href="https://theconversation.com/giant-firms-have-a-hidden-borrowing-advantage-that-has-helped-keep-them-on-top-for-decades-new-research-153001">historically disadvantaged</a> when it comes to borrowing, which concentrated power in the hands of larger corporations. He’s worried we’ll see a K-shaped recovery, which will exacerbate the divergence in fortunes between small and large companies even further. </p>
<p>Hager tells us that since the pandemic first hit, larger corporations have seen their profitability restored and financial conditions improve, “whereas smaller corporations are heading in the opposite direction”.</p>
<p>In our second story, we hear about a new technique to protect endangered birds whose nests are often attacked by invasive predators. Scientists used fake smells to trick predators such as ferrets and hedgehogs into ignoring the birds’ eggs. Catherine Price, postdoctoral researcher in conservation biology at the University of Sydney, who worked on a study testing out the idea in the Mackenzie Basin on New Zealand’s South Island, explains what they did – and <a href="https://theconversation.com/scientists-used-fake-news-to-stop-predators-killing-endangered-birds-and-the-result-was-remarkable-152320">just how successful it was</a>. </p>
<p>And Luthfi Dzulfikar, associate editor at The Conversation in Indonesia, gives us his recommended reads. </p>
<p>The Conversation Weekly is produced by Mend Mariwany and Gemma Ware, with sound design by Eloise Stevens. Our theme music is by Neeta Sarl. You can find us on Twitter <a href="https://twitter.com/TC_Audio">@TC_Audio</a>, on Instagram at <a href="https://www.instagram.com/theconversationdotcom/?hl=en">theconversationdotcom</a>. or via email on podcast@theconversation.com. You can also sign up to <a href="https://theconversation.com/newsletter?utm_campaign=PodcastTCWeekly&utm_content=newsletter&utm_source=podcast">The Conversation’s free daily email here</a>.</p>
<p>A transcript of this episode <a href="https://theconversation.com/concern-is-mounting-about-zombie-companies-why-that-matters-for-the-economic-recovery-158554">is available here.</a></p>
<p>News clips in this episode are from <a href="https://www.youtube.com/watch?v=_mbMCQBFkCU">ABC</a> <a href="https://www.youtube.com/watch?v=CbVC2yUKVeo">News</a>, <a href="https://www.youtube.com/watch?v=LAFuyCRqta0">CNBC</a>, <a href="https://www.youtube.com/watch?v=zmnwucyX27Y">CNBC TV</a>, <a href="https://www.youtube.com/watch?v=HNIViibimVU">DW News</a>, <a href="https://www.youtube.com/watch?v=Avbxm89-MA0">Arirang</a>, <a href="https://www.youtube.com/watch?v=7VMNOqI-cyo">ECB</a> <a href="https://www.youtube.com/watch?v=pKpX_uWjFIU">News</a>, <a href="https://www.youtube.com/watch?v=Ci4Q3Whongk">CNA</a>, <a href="https://www.youtube.com/watch?v=VlL3C-xP_KI">eNCA</a> and <a href="https://www.youtube.com/watch?v=8vgCPyAFIac">Bloomberg News</a>. </p>
<p><em>You can listen to The Conversation Weekly via any of the apps listed above, our <a href="https://feeds.acast.com/public/shows/60087127b9687759d637bade">RSS feed</a>, or find out how else to <a href="https://theconversation.com/how-to-listen-to-the-conversations-podcasts-154131">listen here</a>.</em></p><img src="https://counter.theconversation.com/content/158544/count.gif" alt="The Conversation" width="1" height="1" />
Plus a new technique to protect birds from predators – using fake smells. Listen to episode 10 of The Conversation Weekly podcast.Gemma Ware, Head of AudioDaniel Merino, Associate Breaking News Editor and Co-Host of The Conversation Weekly PodcastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1516722021-03-01T13:16:26Z2021-03-01T13:16:26ZWhy do flowers smell?<figure><img src="https://images.theconversation.com/files/376865/original/file-20201231-17-b5tlb0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A floral scent can be enjoyable for a person, but it has an important job for the flower.</span> <span class="attribution"><span class="source">Richard L. Harkess</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do flowers smell? – Henry E., Age 9, Somerville, Massachusetts</strong></p>
</blockquote>
<hr>
<p>Imagine walking through a tropical forest as a sweet scent wafts through the air. A little farther down the path, the putrid stench of rotting flesh makes you catch your breath. Upon investigation, you find that both odors originate from flowers – but why do flowers smell like anything at all?</p>
<p>It’s actually part of a strategy that helps flowering plants reproduce themselves and spread their species. Certain scents help these flowers solve a big problem.</p>
<p>Plants flower to produce seeds that can go on to become new plants. To make a viable seed, pollen from one part of the flower must <a href="https://www.fs.fed.us/wildflowers/pollinators/What_is_Pollination/">fertilize the ovules</a> in another part of the flower. <a href="https://www.fs.fed.us/wildflowers/pollinators/What_is_Pollination/birdsandbees.shtml">Some plants can self-pollinate</a>, using their own pollen to fertilize the ovule. Others require pollen from another plant of the same species – that’s called <a href="https://www.fs.fed.us/wildflowers/pollinators/What_is_Pollination/birdsandbees.shtml">cross-pollination</a>.</p>
<p>So how does one plant get some other individual plant’s pollen where it needs to be?</p>
<p>Sometimes gravity helps pollen fall into place. Sometimes wind carries it. Wind-pollinated flowers, like those of many trees and grasses, don’t produce a scent.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Bee transfers pollen from one blossom to another" src="https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/382302/original/file-20210203-21-1afen3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Animal pollinators can carry pollen from one flower’s stigma to another flower’s ovule as they forage for food.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/the-process-of-cross-pollination-with-bee-royalty-free-illustration/1060121100">ttsz/iStock via Getty Images Plus</a></span>
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<p>Other flowers are pollinated by birds, bats, insects or even small rodents carrying the pollen from one flower to another. In these cases, the flowers might provide a little incentive. <a href="https://www.esa.org/blog/2018/04/04/vertebrate-polinator-metaanalysis/">Animal pollinators are rewarded</a> by sweet energy- and nutrient-rich nectar or protein-packed pollen they can eat.</p>
<p>Flowers that need the help of insects and bats go one step further, producing a floral scent that acts as a smelly kind of welcome sign for just the right pollinator.</p>
<p>An orchid blooming in the tropical forest or a rose in your garden needs to attract a pollinator to bring pollen from flowers of the same species. However, there are flowers which look similar but are from other species. To differentiate itself from other flowers, each species’ flowers puts out a unique scent to attract specific pollinators.</p>
<p>Similar to the perfumes at a department store counter, flower scents are made up from a large and diverse number of chemicals which evaporate easily and float through the air. The type of chemical, its amount and its interaction with other chemicals give the flower its unique scent. The <a href="https://www.smithsonianmag.com/smart-news/why-do-flowers-smell-good-349826/">scent of a rose</a> may consist of as many as 400 different chemicals.</p>
<p>People can smell these floral scents because they easily evaporate from the flower, drifting on the air currents to attract pollinators. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="corpse flower blossom in a greenhouse" src="https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/382303/original/file-20210203-21-8gnlyv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The giant corpse flower has a very stinky scent that its pollinators love.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/titan-arum-royalty-free-image/911610946">Photography by Mangiwau/Moment via Getty Images</a></span>
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</figure>
<p>Flower fragrances may be sweet and fruity, or they can be musky, even stinky or putrid depending on the pollinator they are trying to attract. A blooming apple or cherry tree emits a sweet scent to attract bumblebees, honeybees and other bees. But stick your nose into the beautiful flowers of a pear tree – a close relative of apples and cherries – and you may recoil in disgust, as these flowers smell musky or putrid to attract flies as pollinators. Similarly, the <a href="https://www.usbg.gov/corpse-flowers-us-botanic-garden">corpse flower</a>, native to Indonesian rainforests, emits a foul odor reminiscent of rotting flesh to attract flies and beetles to pollinate its flowers.</p>
<p>Moths and bats flying at night locate flowers by the scent some release after the Sun goes down. The night-blooming cereus, the saguaro cactus and the dragon fruit all have large white flowers which open at night – they seem to glow in the moonlight, making them visible to nocturnal visitors. Their strong perfume helps guide pollinators inside. While drinking the sweet nectar, the pollinator picks up pollen which it then deposits in the next flower visited.</p>
<p>Once pollinated, the flower stops producing a floral scent and nectar and redirects its energy to the fertilized embryo that will become the seed.</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/151672/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Harkess has received funding from USDA/NIFA. </span></em></p>Not all flowers smell good, to people at least, but their scents are a way to attract pollinators.Richard L. Harkess, Professor of Floriculture and Ornamental Horticulture, Mississippi State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1535682021-01-28T13:44:21Z2021-01-28T13:44:21ZMale butterflies mark their mates with a stench to ‘turn off’ rival suitors<p>Smells, scents and stenches are a common feature in the messy world of sex. In animals, aromas such as pheromones are often used to attract and charm potential mates. But some male butterflies use sex smells for another purpose entirely: to <a href="https://science.sciencemag.org/content/193/4251/419.abstract">deposit a stench on their coital partner</a> so foul that other potential suitors will give her a wide berth.</p>
<p>This jealous behaviour from one of nature’s most beloved insects is not without precedent. A previous study found that some male butterflies effectively slap a “<a href="https://academic.oup.com/sysbio/advance-article-abstract/doi/10.1093/sysbio/syaa070/5901062?redirectedFrom=fulltext">chastity belt</a>” on their mates, plugging their sexual organs to hamper the attempts of other males to mate with the female.</p>
<p>And although a stink is perhaps a less permanent parting gift than a genital plug, it’s still motivated by the same key evolutionary incentive: male butterflies will be favoured by natural selection if it’s their sperm that is fertilised in a female – not that of their rivals. </p>
<p>Turning off other males with a smelly signal ensures the male butterfly’s paternity – giving other suitors cause to take wing and avoid the newly impregnated female. The smell might also benefit the female, who can safely store sperm from the first male while avoiding costly harassment from other males.</p>
<p>What’s particularly striking about the chemical that produces this post-coital stink – identified some years ago as a compound called <a href="https://link.springer.com/article/10.1007/s10886-007-9393-z">beta-ocimene</a> – is that it occurs in flowering plants as well as in butterflies. </p>
<p>For years, this has puzzled researchers. How is the very same chemical compound produced by plants and butterflies – two very distantly related species? Our <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001022">recent study</a> used genome mapping (which reveals the DNA sequence of an organism) to answer this question. In doing so, we identified a novel gene that produces beta-ocimene in butterflies, entirely distinct from those known in plants.</p>
<h2>Several smells</h2>
<p>While it’s unusual for insects to produce chemical compounds found in plants, it’s also important to highlight that different butterfly species have access to a vast arsenal of different smelly compounds. </p>
<p>Our <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001022">study</a> involved the South American butterfly genus known as <a href="http://www.heliconius.org/"><em>heliconius</em></a>, in which even closely related species deploy a different type of chemical bouquet on their female partner. </p>
<p>The existence of this wide range of smells suggests rapid evolution – a quick turnover of pongs, stinks and stenches in the <em>heliconius</em> genus. In the wild, these smells battle for dominance, with the stinkiest odour resulting in the fewest males “trying it on” with an already-mated female. </p>
<h2>Sequencing a stench</h2>
<p>We know that the smelly beta-ocimene compound is not found in all <em>heliconius</em> butterflies. For instance, it’s present in <em>heliconius melpomene</em> butterflies, but not the closely related <em>heliconius cydno</em> butterfly. We realised that mating these butterflies, and examining which smell their offspring used, would help us understand how these smells evolve.</p>
<p>The first step of this project began at the <a href="https://stri.si.edu/">Smithsonian Tropical Research Institute</a> in Panama, in a small town on the Panama Canal called Gamboa. We mated the two species of butterfly to create hybrids, analysed the smelly chemicals produced by these hybrids, and sequenced their genomes to create a complete map of their DNA.</p>
<p>This approach, known as “quantitative trait locus mapping”, allowed us to identify a section of the butterfly’s genome associated with pheromone production – the gene at the source of the smells.</p>
<p>We then transferred this gene into simple bacteria, which happen to use a very similar genetic code to insects. The bacteria with the smelly gene were then tested in a controlled chemical environment, to see if they would produce the beta-ocimene we so often see in flowering plants.</p>
<p>In performing this experiment, <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001022">we identified a novel gene, <em>HMEL ocimene synthase</em></a>, which produces beta-ocimene in <em>heliconius melpomene</em> butterflies in a completely different way to how it’s produced in plants. This gene is in no way related to the plant genes we already know to produce beta-ocimene. </p>
<p>The independent evolution of the same trait in plants and insects – in this case, pheromone production – helps us understand evolution a little better.</p>
<p>And, while beta-ocimene is produced by plants to tempt insects towards their pollen-rich flowers, it’s deployed by male butterflies to ward off rivals in the rancid game of butterfly love – showing that, when it comes to smells, context really is everything.</p><img src="https://counter.theconversation.com/content/153568/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Jiggins receives funding from European Research Council, BBSRC and NERC. </span></em></p><p class="fine-print"><em><span>Kathleen Darragh received funding from NERC (Natural Environment Research Council) and STRI (Smithsonian Tropical Research Institute). </span></em></p>The stench was once thought to originate from plants, but scientists have now pin-pointed its true origin.Chris Jiggins, Professor of Evolutionary Biology, University of CambridgeKathleen Darragh, Postdoctoral Research Associate, University of California, DavisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1414042020-08-06T10:17:05Z2020-08-06T10:17:05ZFour reasons why some people become ‘super smellers’ – from pregnancy to genetic differences<figure><img src="https://images.theconversation.com/files/351273/original/file-20200805-24-z254sc.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C7940%2C5304&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some super smellers even associate unpleasant memories or feelings of annoyance with certain smells. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/young-african-american-woman-wearing-denim-1477639214">Shift Drive/ Shutterstock</a></span></figcaption></figure><p>Do certain smells make you feel uncomfortable, even nauseous? Or is your nose so good that you can detect even the subtlest aromas in your favourite wine? Perhaps certain smells evoke negative or positive feelings? If you answered yes to any of these questions, you might just be a “super smeller”.</p>
<p>Medically known as <a href="https://www.sciencedirect.com/topics/neuroscience/hyperosmia">hyperosmia</a>, super smellers are people who have a heightened sense of smell compared to the average person. Some super smellers may be more sensitive to pleasant smells, while others may be more affected by unpleasant odours. </p>
<p>Hyperosmia is <a href="https://www.sciencedirect.com/topics/neuroscience/hyperosmia#:%7E:text=Hyperosmia%20(heightened%20smell%20function)%20is,below%20those%20of%20normal%20subjects">relatively rare</a>, so there’s still much that researchers don’t know about the condition. However, here are some of the reasons a person may have hyperosmia.</p>
<h2>1. Health conditions</h2>
<p>A number of studies have reported links between various medical conditions and hyperosmia, including <a href="https://pubmed.ncbi.nlm.nih.gov/25098475/">Lyme Disease</a>, <a href="https://link.springer.com/article/10.1007/BF00313864">migraines</a>, <a href="https://pubmed.ncbi.nlm.nih.gov/11186713/">body fluid</a> <a href="https://pubmed.ncbi.nlm.nih.gov/6442085/">disturbances</a>, <a href="https://www.sciencedirect.com/science/article/abs/pii/S0163834312002186">hormone deficiency</a> and <a href="https://link.springer.com/article/10.2165/00003495-198020020-00006">certain</a> <a href="https://www.ncbi.nlm.nih.gov/pubmed/32106138">medications</a>. Though it’s not fully understood what leads to hyperosmia in these cases, it could possibly be the effect these diseases have on the body’s electrolytes, thus affecting the signals generated at the scent receptors.</p>
<p>Studies have also shown that certain <a href="https://link.springer.com/article/10.1007/s13353-014-0252-7">genetic conditions</a> such as duplication or overexpression of the <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/kal1-gene">KAL1 gene</a> – which produces a protein (anosmin-1) that appears to control the growth and movement of nerve cells that help process smell – and other genetic <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/ejp.1272">mutations</a> are linked to heightened sense of smell. </p>
<p>One study even showed that the genetic coding for a certain protein that helps to <a href="https://www.ncbi.nlm.nih.gov/pubmed/25480730">bind on to smells</a> and help them reach the smell receptors in the nose, does vary in a population, so some people may naturally have a better sense of smell than others.</p>
<h2>2. Pregnancy</h2>
<p>Many women who become pregnant often claim certain smells which never used to bother them suddenly become revolting. And one review has actually confirmed that some pregnant women do temporarily become super smellers. </p>
<p>By comparing the findings of more than 50 studies into how pregnancy alters sense of smell, researchers concluded that although pregnant women didn’t have higher smell intensity overall, they were possibly <a href="https://www.frontiersin.org/articles/10.3389/fpsyg.2014.00067/full7">more sensitive to certain odours</a>. But there wasn’t enough evidence to determine if their ability to identify more odours in general had increased.</p>
<figure class="align-center ">
<img alt="Man eating food on bed while pregnant women covers nose." src="https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=511&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=511&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351274/original/file-20200805-290-9rjse0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=511&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Typically, these ‘super smelling’ abilities are only temporary.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/heightened-sense-smell-during-pregnancy-pregnant-1583458078">Prostock-studio/ Shutterstock</a></span>
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</figure>
<p>Despite being such a commonly reported phenomenon, researchers still aren’t entirely sure why this happens. However, this sensitivity is typically temporary, rather than a permanent change.</p>
<h2>3. Brain differences</h2>
<p>A 2019 study aimed to uncover whether the brains of super smellers worked differently than normal. Researchers compared 25 men who <a href="https://link.springer.com/article/10.1007/s11682-018-0008-9">considered themselves super smellers</a> with 20 men who rated their sense of smells as normal. Using brain scans, the researchers compared the grey matter volume in parts of the brain associated with smell.</p>
<p>They found that in super smellers there was increased brain activity in two key areas responsible for bringing together smell information, and learning and memorising smells. But while research detected these brain differences, the researchers were unable to ascertain whether this was caused by genetics, or if it was learned. </p>
<p>It is well established that smell and memory are strongly linked. But the findings of a 2014 study suggest that this may be the <a href="https://journals.sagepub.com/doi/10.1177/1359105313481080">basis for hyperosmia</a>. The study looked at 55 volunteers who rated their sense of smell as better than average. They compared them to a group of people the same ages and gender who considered their sense of smell to be normal.</p>
<p>The super smellers in this study were asked to complete a structured questionnaire about their experiences of environmental smells. They associated certain smells such as fragrances and human body products (such as sweat) with negative consequences and unpleasant memories, and found that environmental smells evoked feelings of annoyance and disgust. But the study didn’t investigate whether participants were also sensitive to other smells, so it’s difficult to know if these volunteers actually had a normal or heightened sense of smell.</p>
<p>Other studies have similarly found that sensitivity to certain smells, including <a href="https://www.ncbi.nlm.nih.gov/pubmed/27221295">phenolic resins</a> (such as formaldehyde) and the shellfish-like pyridine odour in <a href="https://academic.oup.com/occmed/article-abstract/56/1/51/1374604">organic chemicals</a>, are linked with negative experiences, suggesting that sensitivity to these smells develops based on negative experiences in the workplace – for example being exposed to chemical odours at work.</p>
<h2>4. Training</h2>
<p>So does being a super smeller convey a super power that lasts continuously, or can it be temporary? </p>
<p>In 2003, I conducted a study with 230 volunteers to test their <a href="https://www.cambridge.org/core/journals/journal-of-laryngology-and-otology/article/superosmic-phenomenon/4D0D83E5A49D994EC6E3C6FD19AC17AE">depth of smell</a> for the smell of phenylethyl alcohol (the smell of roses) or eucalyptol (a mint-like smell). The depth of smell relates to how small a concentration of an odour can be detected (known as the “threshold”). We used a custom-built device that delivered eight concentrations of the smells, from barely detectable to very strong. </p>
<p>We found that 2% of the group demonstrated what we dubbed as “the superosmic phenomenon” on single testing. A further 10% demonstrated this phenomenon on various occasions during repeated testing (where the test was performed ten times on separate occasions at one-week intervals). This phenomenon occurred when the volunteers were able to detect the smells at three or more levels below where they would normally detect it – and they were able to continue detecting the smells at least ten times during the test. The test was performed once a week over a period of ten weeks.</p>
<p>In almost all cases where the superosmia occurred, this was followed by a sudden, rapid loss of smell detection at this lower level before the end of the test. So without any explanation for why, we could see evidence of short-term super smellers when focused on certain smells.</p>
<p>Overall, the assumption all super smellers achieve their “superpower” because of their genes or a rare medical condition is probably unlikely. Think about sommeliers or perfumers – these people train their noses to be able to recognise many unique smells. In fact, smell training can even allow people who have suffered smell loss to recover their <a href="http://www.fifthsense.org.uk">sense of smell</a>.</p>
<p>It seems that super smellers are a mixture of people who may be genetically wired to smell better, some who train to smell better and some who have an underlying medical condition. And others, perhaps including pregnant women, they may only experience smell sensitivity – not true hyperosmia.</p><img src="https://counter.theconversation.com/content/141404/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carl Philpott receives funding from the National Institute of Health Research. He is affiliated with Fifth Sense. </span></em></p>Hyperosmia is relatively rare, but there are many reasons a person might develop this condition – even temporarily.Carl Philpott, Professor of Rhinology and Olfactology, University of East AngliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1250372019-11-04T12:12:57Z2019-11-04T12:12:57ZWhy do feet stink by the end of the day?<figure><img src="https://images.theconversation.com/files/299913/original/file-20191101-88428-e37hgp.jpg?ixlib=rb-1.1.0&rect=485%2C0%2C2540%2C1882&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Keep those stinkers away!</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/woman-smelly-feet-1131532760">leungchopan/Shutterstock.com</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>.</em></p>
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<blockquote>
<p><strong>Why do feet stink by the end of the day? – Helen E., age 6, Somerville, Massachusetts</strong></p>
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<hr>
<p>When I was a kid, our family would end the day by relaxing in front of the TV after dinner. Everyone would have a seat, take off their shoes and put up their feet. Before long, a strange and unsavory aroma invaded our noses. Sometimes our feet smelled so bad that my dad would joke, “Who cut the cheese?”</p>
<p>That seems like an odd thing to say, because cheese tastes good! But some cheeses, like <a href="https://www.cheese.com/limburger/">Limburger cheese</a>, smell nasty. When it is cut, many people hold their nose and run for the hills.</p>
<p>But people running to escape the stench of Limburger cheese may be in for an unpleasant surprise when they take their sneakers off later. All that running would make their feet sweat, and sweaty feet often reek like smelly cheese.</p>
<p>What’s the connection?</p>
<p>It comes down to a type of <a href="https://www.britannica.com/science/bacteria/The-importance-of-bacteria-to-humans">bacteria</a> called <em>Brevibacterium linens</em>. Bacteria are very tiny creatures that can be seen only with a microscope. There are many different kinds of bacteria found all over the world, including inside your body and on your skin. Some of these bacteria are germs that can make you sick, but most do not cause harm and can even be helpful.</p>
<p><em>Brevibacterium linens</em> are harmless bacteria found on people’s skin – they eat up skin cells that have died. Normally, these bacteria do not produce much of an odor because there aren’t too many of them.</p>
<p>But when you wear shoes, your feet get warm and moist. Your foot sweat contains salt, which these bacteria love. Under these conditions, a little <em>Brevibacterium linens</em> can become a lot of <em>Brevibacterium linens</em> munching on your feet.</p>
<p>And like anything else that eats, <a href="https://doi.org/10.1016/B978-0-08-100596-5.00632-6">these bacteria make smelly waste</a>. It is their waste that gives sweaty feet their funky odor: It contains stinky chemicals like those made by skunks and rotten eggs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/299914/original/file-20191101-88372-6i7l1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bacteria contribute the stink of their waste to the overall odor of some cheeses as well.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/piece-belgian-limburger-cheese-on-board-309618497">picturepartners/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>When people make cheese like Limburger, some of the <em>Brevibacterium linens</em> bacteria on their skin get <a href="https://doi.org/10.1016/B978-0-08-100596-5.00675-2">left behind on the cheese</a>. These bacteria aren’t picky eaters, so they’ll start gobbling up the surface of the cheese. As the bacteria eat the cheese, they make the shell around the cheese, <a href="https://www.specialtyfood.com/news/article/cheese-rinds-101/">called the rind</a>. And they produce the same foul-smelling waste.</p>
<p>This is why feet can smell like cheese – they both have the same bacteria living on them. Other kinds of bacteria eat cheese too, and they make different chemicals that give the various cheeses their unique odors and flavors.</p>
<p>Because foot stench and cheese stench have the same source, some scientists have come up with a sneaky idea. Mosquitoes zero in on people by sensing these chemicals our skin bacteria produce. Researchers are experimenting with <a href="https://doi.org/10.1016/0169-4758(96)10002-8">using Limburger cheese to trick the insect pests</a> and lure them into traps so they can’t bite people.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/299915/original/file-20191101-88403-1f1i23w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">There are ways to cut down on the stink.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/male-smelly-foot-colorful-visible-odor-1293754405">Ezume Images/Shutterstock.com</a></span>
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<p>Remember all this next time everyone’s relaxing, shoes and socks off, toes free. If someone’s little piggies smell like they went to market and bought a ton of stinky cheese, now you can explain what’s going on.</p>
<p>And don’t worry: Other than the offensive smell, stinky feet won’t hurt you. <a href="https://health.clevelandclinic.org/4-sure-fire-ways-you-can-avoid-stinky-feet/">To get rid of the odor</a>, keep them clean and dry. Wear fresh socks and use powder to absorb the sweat that skin bacteria need to grow. </p>
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<p class="fine-print"><em><span>Bill Sullivan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Sweaty feet and certain cheeses have something in common that makes them reek – can you guess what it is?Bill Sullivan, Professor of Pharmacology & Toxicology, Indiana UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1047722018-11-05T18:46:27Z2018-11-05T18:46:27ZCurious Kids: How do we smell?<figure><img src="https://images.theconversation.com/files/240737/original/file-20181016-165909-1rvfclo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The sense of smell helps us know what and where things are, like yummy food. R. Suarez.</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky! You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
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<p><strong>How do we smell? – Audrey, age 6, Brisbane.</strong></p>
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<p>Audrey, you have asked a question that humans have wondered about for centuries. And it’s only pretty recently we have started to really understand the answer. </p>
<p>Whenever we smell something, our nose and brain work together to make sense of hundreds of very tiny invisible particles, known as molecules or chemicals, that are floating in the air. If we sniff, more of these molecules can reach the roof of our nostrils and it is easier to smell a smell. </p>
<p>The fact that we have two nostrils allows our brain to detect small differences in the number of molecules that reach each one, so we can follow a smell trail just like tracker dogs. Have you ever tried finding where a smell is coming from? See how hard it gets with one nostril blocked.</p>
<p>The sense of smell also help us taste food. That is why food tastes bland whenever your nose is blocked.</p>
<p>Inside your nostrils, there are tiny things called neurons that “talk” to each other using electrical messages (our brains are mostly made of neurons too, by the way).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=623&fit=crop&dpr=1 600w, https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=623&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=623&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=783&fit=crop&dpr=1 754w, https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=783&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/240747/original/file-20181016-165897-1twh4z1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=783&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Olfactory neurons (green, blue and red), located at the roof of the nostrils, recognise molecules and send electrical signals to neurons in the olfactory bulb (yellow). R. Suárez.</span>
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<h2>Smell memories</h2>
<p>These type of tiny cells, called olfactory neurons (olfaction means smell), have long cable-like connections that send electrical messages to a spot at the front of the brain, known as the olfactory bulb. Each olfactory neuron connects with a different neuron in the olfactory bulb, which then sends this information to other areas of the brain. </p>
<p>The parts of the brain that get these signals also do other things, such as storing memories or provoking emotions. That is why some smells can bring back old memories. </p>
<p>Even some older adults can remember the smell of their kindy class, or their grandparent’s house. Also, some smells can make us feel scared or happy, such as the smells of smoke or flowers. For example, the smell of freshly mowed lawn can help us relax.</p>
<p>Do you have nice memories of a place or food that you have smelt in the past?</p>
<h2>How animals smell</h2>
<p>The sense of smell is very important to almost all animals, as it helps them find food, recognise family members, and avoid danger. </p>
<p>For example, the nostrils of fish and sharks let them smell underwater, even though they breathe water through their mouths and gills. Some animals, like dolphins and whales, have lost the sense of smell as, over millions of years, their nostrils have moved to the top of their heads and evolved into blowholes. </p>
<p>The way smells are felt by the nose and brain is very similar in all animals. Even the way olfactory neurons work is also very similar to that of insects (but insects smell using their antennae, not with nostrils).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=327&fit=crop&dpr=1 600w, https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=327&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=327&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/240746/original/file-20181016-165894-1tltf9z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The sense of smell works in similar ways in both vertebrates (mouse olfactory bulb in orange) and invertebrates (moth antenna in orange). R Suárez.</span>
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<p>The way the brain deals with smells is very different to how it deals with other senses, such as seeing and hearing. For example, we can identify the different instruments playing in a band, or the different shapes and colours in a painting. But it is very hard for us to tell the individual parts of a smell mixture. </p>
<p>We can feel the smell “orange” or “coffee” as a single thing, but have trouble identifying the many different parts that make up those smells individually. However, it is possible to get better at this with practice. Professional wine-tasters or perfume-makers can detect more parts of a smell mixture than most people.</p>
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Read more:
<a href="https://theconversation.com/curious-kids-whats-it-like-to-be-a-fighter-pilot-100563">Curious Kids: what's it like to be a fighter pilot?</a>
</strong>
</em>
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p class="fine-print"><em><span>Rodrigo Suarez receives funding from the Australian Research Council. </span></em></p>The parts of the brain that get ‘smell signals’ from the nose also do other things, such as storing memories or provoking emotions. That is why some smells can bring back old memories.Rodrigo Suarez, ARC DECRA Research Fellow, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1015072018-08-27T10:47:25Z2018-08-27T10:47:25ZWhy you can smell rain<figure><img src="https://images.theconversation.com/files/233335/original/file-20180823-149463-1y5q7lw.jpg?ixlib=rb-1.1.0&rect=290%2C231%2C3661%2C2393&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Your nose knows what's on the way.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/LYq7W1lRal4">Lucy Chian/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em><a href="https://theconversation.com/por-que-sentimos-el-olor-de-la-lluvia-102529">Leer in español</a></em>.</p>
<p>When those first fat drops of summer rain fall to the hot, dry ground, have you ever noticed a distinctive odor? I have childhood memories of family members who were farmers describing how they could always “smell rain” right before a storm.</p>
<p>Of course rain itself has no scent. But moments before a rain event, an “earthy” smell known as petrichor does permeate the air. People call it musky, fresh – generally pleasant.</p>
<p>This smell actually comes from the moistening of the ground. Australian scientists first documented the <a href="https://doi.org/10.1038/201993a0">process of petrichor formation in 1964</a> and scientists from the Massachusetts Institute of Technology further <a href="https://doi.org/10.1038/ncomms7083">studied the mechanics of the process</a> in the 2010s.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/233537/original/file-20180824-149484-mciivu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Petrichor’s main ingredients are made by plants and bacteria that live in the ground.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/green-seedling-growing-on-ground-rain-265568735">vovan/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Petrichor is a combination of fragrant chemical compounds. Some are from oils made by plants. The main contributor to petrichor are <a href="http://eol.org/pages/7861/overview">actinobacteria</a>. These tiny microorganisms can be found in rural and urban areas as well as in marine environments. They decompose dead or decaying organic matter into simple chemical compounds which can then become nutrients for developing plants and other organisms.</p>
<p>A byproduct of their activity is an organic compound <a href="https://www.thoughtco.com/can-you-smell-rain-geosmin-and-petrichor-607587">called geosmin</a> which contributes to the petrichor scent. Geosmin is a type of alcohol, like rubbing alcohol. Alcohol molecules tend to have a strong scent, but the complex chemical structure of geosmin makes it especially noticeable to people even at extremely low levels. Our noses can detect just a few parts of geosmin per trillion of air molecules.</p>
<p>During a prolonged period of dryness when it has not rained for several days, the decomposition activity rate of the actinobacteria slows down. Just before a rain event, the air becomes more humid and the ground begins to moisten. This process helps to speed up the activity of the actinobacteria and more geosmin is formed.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/233541/original/file-20180824-149481-14ys448.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Before you see it, do you smell it?</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/starting-rain-1094204522">elisa galceran garcia/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>When raindrops fall on the ground, especially porous surfaces such as loose soil or rough concrete, they will splatter and <a href="https://youtu.be/Waqmq_GTyjA">eject tiny particles called aerosols</a>. The geosmin and other petrichor compounds that may be present on the ground or dissolved within the raindrop are released in aerosol form and carried by the wind to surrounding areas. If the rainfall is heavy enough, the petrichor scent can travel rapidly downwind and alert people that rain is soon on the way.</p>
<p>The scent eventually goes away after the storm has passed and the ground begins to dry. This leaves the actinobacteria lying in wait – ready to help us know when it might rain again.</p><img src="https://counter.theconversation.com/content/101507/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tim Logan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A weather expert explains where petrichor – that pleasant, earthy scent that accompanies a storm’s first raindrops – comes from.Tim Logan, Instructional Assistant Professor of Atmospheric Sciences, Texas A&M UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/946962018-05-04T10:47:32Z2018-05-04T10:47:32ZThat distinctive springtime smell: Asparagus pee<figure><img src="https://images.theconversation.com/files/217076/original/file-20180501-135837-1nmkwlg.jpg?ixlib=rb-1.1.0&rect=178%2C0%2C2693%2C1781&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">One of the signature fragrances of spring comes after the consumption of asparagus.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/s7stem/5169230033">Anton G</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Along with many other delights, springtime brings the beginning of the asparagus growing season. Regardless of whether you prefer the green, purple or white variety, asparagus provides a rich source of vitamins and minerals, and its consumption as part of a healthy diet may <a href="https://doi.org/10.3390/nu8030156">reduce risk of cancer</a> and <a href="https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/vitamins/vitamin-b/">cardiovascular-related diseases</a>.</p>
<p>Despite the nutritional benefits of asparagus, many are opposed to eating the vegetable due to its pungent aftereffects. As <a href="https://www.penguinrandomhouse.com/books/86757/fart-proudly-by-benjamin-franklin/9781583940792/">Benjamin Franklin wrote in 1781</a>, “A few stems of asparagus eaten, shall give our urine a disagreable odour.” This odor has become so well known that post-consumption urine is now often referred to as “asparagus pee.”</p>
<p>Scientists believe the odor in question is <a href="https://doi.org/10.1126/science.1162354">due to two chemicals</a>: methanethiol and S-methyl thioester. When enzymes in the human digestive tract break down the asparagusic acid that’s naturally present in the vegetable, these volatile compounds are created. When voided from the body, they become foul-smelling gas, wafting up from your asparagus pee.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=896&fit=crop&dpr=1 600w, https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=896&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=896&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1126&fit=crop&dpr=1 754w, https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1126&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/217342/original/file-20180502-153891-1nq8o8k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1126&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ready for harvest.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/fresh-green-asparagus-growing-on-garden-12506143">DUSAN ZIDAR/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>And <a href="https://doi.org/10.1093/chemse/bjq081">just because you don’t smell it</a> <a href="https://doi.org/10.1136/bmj.281.6256.1676">doesn’t mean you’re not making it</a>. Two studies have shown that people who are unable to smell the odor in their own urine also don’t detect it in the urine of known producers. Yes, volunteers sniffed samples of other people’s asparagus pee. Though most everyone probably produces the scent to some degree, it seems <a href="https://doi.org/10.1136/bmj.281.6256.1676">not everyone’s noses pick up on it</a>.</p>
<p>In fact, a study my colleagues and I conducted in 2017 <a href="https://doi.org/10.1136/bmj.i6071">found that only 40 percent</a> of those surveyed reported detecting the odor in their urine. A lower proportion of women were able to detect the odor, compared to men, despite <a href="https://doi.org/10.1016/0028-3932(89)90055-9">women being thought to have</a> a <a href="https://doi.org/10.1016/0028-3932(85)90067-3">more keen sense of smell</a>.</p>
<p>We asked almost 7,000 participants from two large cohort studies to respond to the prompt “After eating asparagus, you notice a strong characteristic odor in your urine.” By linking the questionnaire data with genetic data, we were able to show that the ability to smell or not to smell depends on a person’s genetic makeup. Hundreds of variants in the DNA sequence across multiple genes involved in sense of smell are strongly associated with the ability to detect asparagus metabolites in urine.</p>
<p>Asparagus isn’t the only food that has genetically linked controversial smell or taste effects. Some people avoid eating cilantro because they claim it has a “soapy” aftertaste. A study using data from almost 30,000 users of 23andMe found <a href="https://doi.org/10.1186/2044-7248-1-22">genetic variants in olfactory receptors</a> linked to people’s perception of this adverse taste.</p>
<p>Maybe you can conduct your own survey at the next family meal that includes a platter of asparagus – or soon after.</p><img src="https://counter.theconversation.com/content/94696/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Coseo Markt receives funding from the National Institutes of Health. </span></em></p>Perhaps you’ve noticed something unusual in the bathroom after you consume this healthy spring vegetable. A Speed Read explains there’s two parts to the stinky puzzle: production and perception.Sarah Coseo Markt, Research Scientist in Epidemiology, T.H. Chan School of Public Health, Harvard UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/924962018-02-28T11:40:24Z2018-02-28T11:40:24ZFrom Smell-O-Vision to Astrocolor, the film industry’s biggest innovation flops<figure><img src="https://images.theconversation.com/files/208143/original/file-20180227-36689-ma984m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Moviegoers familiarize themselves with the joystick that will allow them to interact with the film 'I’m Your Man' during its premiere on Dec. 16, 1992.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Watchf-AP-A-NY-USA-APHS427527-Premiere-of-the-W-/6fc67f2b6ab34b108b5aad744545c301/1/0">AP Photo/Richard Harbus</a></span></figcaption></figure><p><em>Editor’s note: IMAX is hugely popular, while virtual reality movies <a href="https://theconversation.com/hollywood-360-how-virtual-reality-is-poised-to-take-on-the-traditional-movie-industry-91426">are gaining steam</a>. But what about film inventions that never took off? When will they get their due?</em></p>
<p><em>Sure, there are the <a href="http://www.razzies.com/index.html">Razzies</a>, which honor the worst acting performances and directing jobs. But there’s no (dis)honor for film innovations that backfired.</em> </p>
<p><em>We asked four film experts to each write about a different flop. Some ideas were on the right track and would eventually be realized in one form or another. But others are probably best relegated to the dustbin of history.</em></p>
<hr>
<h2>First motion, then sound, then … smell?</h2>
<p><strong>Leo Braudy, University of Southern California</strong> </p>
<p>In the 1950s, the popularity of <a href="https://hypertextbook.com/facts/2007/TamaraTamazashvili.shtml">television exploded</a>, and the film industry started experimenting with technologies to lure audiences back into movie theaters. </p>
<p>In this context, two 1959 olfactory innovations – AromaRama and Smell-O-Vision – emerged. </p>
<p>Both psychology and neurology have shown how closely <a href="https://www.psychologytoday.com/blog/brain-babble/201501/smells-ring-bells-how-smell-triggers-memories-and-emotions">smell is related to memory and emotion</a>. But the orchestration of smell in a “smell story” or “smell movie” is another matter. </p>
<p>AromaRama involved pumping scents <a href="http://www.nationalboardofreview.org/2014/01/innovations-cinema-aromarama/">through an air-conditioning system</a>, while Smell-O-Vision’s <a href="http://www.cabinetmagazine.org/issues/64/turner.php">30 odors</a> were released from vents placed underneath the seats.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=865&fit=crop&dpr=1 600w, https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=865&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=865&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1087&fit=crop&dpr=1 754w, https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1087&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/207936/original/file-20180226-120971-1b7mk13.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1087&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">First they moved, then they talked, now they … smell?</span>
<span class="attribution"><a class="source" href="https://3.bp.blogspot.com/-wIVhpWyr6FI/Vy0DUCU1shI/AAAAAAAAqTQ/NaNJf8sf9VcfK3fA9GpAcTuI1t0YKZfgACLcB/s1600/scentofmystery_poster.gif">Michael Todd, Jr.</a></span>
</figcaption>
</figure>
<p>For budding smell entrepreneurs, the reviews couldn’t have been encouraging. </p>
<p>After New York Times film reviewer Bosley Crowther emerged from his first AromaRama experience, he wrote that he “happily filled his lungs with that lovely fume-laden New York ozone. It never has smelled so good.”</p>
<p>I saw AromaRama’s “<a href="http://www.imdb.com/title/tt0050733/?ref_=fn_al_tt_1">Behind the Great Wall</a>” and Smell-O-Vision’s “<a href="http://www.imdb.com/title/tt0054271/?ref_=nv_sr_1">The Scent of Mystery</a>” during their brief runs in New York, and the only scents I can recall are the pungent smell of an orange being sliced and the dank odor of a Chinese bay.</p>
<p>Instead of enhancing the cinematic experience, the smells ended up supplying something briefly weird and not very interesting, no different from a noisy special effect.</p>
<p>In 1981, filmmaker John Waters satirically revived the technique for his film “<a href="http://www.imdb.com/title/tt0082926/">Polyester</a>,” dubbing it “Odorama.” </p>
<p>Waters sidestepped the expensive scent distribution systems of his predecessors by creating a simple <a href="http://www.zekefilm.org/wp-content/uploads/2016/06/polyster-4.jpg">scratch-and-sniff card</a> that would be cued by numbers on screen. The 10 smells – which included roses (#1), farts (#2) and pizza (#4) – tried valiantly to be distinct. But to me they all vaguely approximated the aroma of oregano.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=490&fit=crop&dpr=1 600w, https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=490&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=490&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=616&fit=crop&dpr=1 754w, https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=616&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/207932/original/file-20180226-140184-1uo8qls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=616&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ‘Odorama’ scratch-and-sniff card.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/altuwa/15597969222">Sébastien Barré</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>Some years later the Los Angeles County Museum had an anniversary showing of “Polyester.” My wife and I had small roles in the film, so we went along. Sure enough, as soon as the show started, almost every member of the packed audience pulled out their treasured scratch-and-sniff cards. </p>
<p>Even though adding odors to movies never took off, at least the connection between smell and memory remained strong.</p>
<hr>
<h2>Letting audiences twist the plot</h2>
<p><strong>Scott Higgins, Wesleyan University</strong></p>
<p>Artists have long sought to erase the boundary between a film and its viewers, and Alejandro Iñárritu’s 2017 <a href="https://variety.com/2017/film/awards/oscars-alejandro-g-inarritus-virtual-reality-installation-carne-y-arena-to-receive-special-award-1202601265/">Oscar-winning</a> virtual reality installation “<a href="http://www.lacma.org/carne-y-arena#landing">Carne y Arena</a>” has come close. </p>
<p>But the dream of putting audiences in the picture has fueled a number of film fiascoes, including an early 1990s debacle called <a href="https://www.youtube.com/watch?v=mx4NeJe9CJI&feature=youtu.be">Interfilm</a>. </p>
<p><a href="http://articles.latimes.com/1992-12-23/news/mn-2336_1_pistol-grip">Billed as a</a> “quantum leap into the future,” Interfilm premiered in December 1992 at the Loews New York multiplex with the short “<a href="http://www.imdb.com/title/tt0171392/?ref_=nv_sr_5">I’m Your Man</a>,” written and directed by inventor Bob Bejan. </p>
<p>It was something like a “<a href="http://mentalfloss.com/article/56160/brief-history-choose-your-own-adventure">Choose Your Own Adventure</a>” book brought to the big screen, courtesy of then cutting-edge <a href="http://cultureandcommunication.org/deadmedia/index.php/Laserdisc">LaserDisc technology</a>. Armrests were outfitted with three-button joysticks. Every few minutes the video would pause and viewers had 10 seconds to vote on one of three choices for the story path. </p>
<p>Even though the movie was only 20 minutes long, it required 90 minutes of footage stored on four laserdisc players <a href="http://www.nytimes.com/1993/01/13/movies/when-the-film-audience-controls-the-plot.html?pagewanted=all">to accommodate the 68 story variations</a>. For a $3.00 admission, viewers could stay through multiple showings and relive the film from different perspectives. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/lS0BSMvRBdA?wmode=transparent&start=40" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A mid-1990s TV ad hypes Interfilm.</span></figcaption>
</figure>
<p>As you might surmise from the lack of joysticks in today’s cinemas, Interfilm’s “quantum leap” got tripped up. </p>
<p>Despite backing from Sony Pictures, few exhibitors were willing to take on the <a href="http://articles.latimes.com/1992-12-23/news/mn-2336_1_pistol-grip">$70,000 cost</a> of retrofitting a single theater. The film was shown in standard definition via <a href="http://www.projectorcentral.com/projectors-evolution.htm">video projection</a>, which couldn’t come close to matching the quality of the 35mm film playing next door. And some audience members would exploit the voting system by racing between vacant seats to cast multiple votes for their preferred storyline. </p>
<p>But the films themselves may have been the biggest stumbling block. Director Bob Bejan shot “I’m Your Man” in less than a week, using his office building as the location. His follow-up, “<a href="http://www.imdb.com/title/tt0113863/?ref_=fn_tt_tt_123">Mr. Payback</a>,” which opened at 44 theaters in 1995, allowed viewers to choose between ways to punish characters: cattle prodding, pants burning or monkey brain eating. </p>
<p>Film critic Roger Ebert <a href="https://books.google.com/books?id=UwXuJCuQ6q4C&lpg=PT258&ots=G4WZjt2swT&dq=roger%20ebert%20%22mass%20psychology%20run%20wild%2C%20with%20the%20mob%20zealously%20pummeling%20their%20buttons%22&pg=PT258#v=onepage&q&f=false">concluded</a> that the “offensive and yokel-brained” “Mr. Payback” was “not a movie” but “mass psychology run wild, with the mob zealously pummeling their buttons, careening downhill toward the sleaziest common denominator.” </p>
<p>That same year, Sony Pictures pulled its support, and shortly thereafter Interfilm was no more. </p>
<hr>
<h2>A giant flying film projector</h2>
<p><strong>Stephen Groening, University of Washington</strong></p>
<p>In the 1960s, American Airlines hired the film equipment manufacturer <a href="https://en.wikipedia.org/wiki/Bell_%26_Howell">Bell & Howell</a> to design an in-flight entertainment system that could compete (and contrast) with TWA’s large single-screen system that had premiered in 1961. </p>
<p><a href="https://www.palgrave.com/us/book/9781844576289">The result was Astrocolor</a>, an in-flight entertainment system featuring a series of 17-inch screens suspended from the luggage rack. </p>
<p>In its promotional campaign, American advertised Astrocolor as “democratic” and <a href="https://youtu.be/cvUFx0ZDbMI">emphasized freedom of choice</a>. Because the screens were positioned every five rows (and every three rows in first class), the set-up didn’t discriminate against those seated in the back of the cabin. And because the screens were small, passengers were free from the tyranny of TWA’s large screen; they could easily decide to not watch the movie and pursue a different activity.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=771&fit=crop&dpr=1 600w, https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=771&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=771&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=969&fit=crop&dpr=1 754w, https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=969&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/207928/original/file-20180226-140197-17z1ood.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=969&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An Astrocolor monitor hangs from the first-class cabin of an American Airlines plane.</span>
<span class="attribution"><span class="source">Courtesy of Special Collections, University of Miami Libraries</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But this was before the advent of the MP4, the DVD, the magnetic videotape and the laserdisc, and airlines needed to use 16mm celluloid prints to exhibit films on board. </p>
<p>So the film was bizarrely threaded along the length of the cabin next to the overhead luggage compartments. Each screen had its own projector that back-projected the film onto the screen in color and in the film’s original aspect ratio. At any given time, nearly 300 feet of film ran through the complex system of gears and loops. </p>
<p>This meant that passengers in the back of the plane saw a scene nearly five minutes after the passengers in the front. And with so many moving parts and a filmstrip that could reach 9,000 feet in length, <a href="https://www.palgrave.com/us/book/9781844576289">the failure rate was 20 percent</a>.</p>
<p>Astrocolor had effectively turned the airplane into a giant film projector, and maintenance of the complex in-flight entertainment system could hinder an airline’s flight schedules.</p>
<p>According to internal documents from Pan American Airlines (which also adopted Bell & Howell’s system), <a href="https://www.routledge.com/MediaSpace-Place-Scale-and-Culture-in-a-Media-Age/Couldry-McCarthy/p/book/9780415291750">the failure rate led to angry passengers and affected crew morale</a>, especially during transatlantic routes. Within a few years, American and Pan Am switched to TransCom’s 8mm film cassette system, and by 1978 Bell & Howell had introduced <a href="https://books.google.com/books?id=8XeCAgAAQBAJ&pg=PA239&lpg=PA239&dq=first+in-flight+VHS+system&source=bl&ots=i_hDYeqhKN&sig=IBkV4Z2TFIF_pBI2POlZD5_Hm1I&hl=en&sa=X&ved=0ahUKEwic1OqO6sbZAhXi5IMKHZcwA9cQ6AEIJzAA#v=onepage&q=first%20in-flight%20VHS%20system&f=false">the first in-flight VHS system</a>.</p>
<p>Even though Astrocolor can be seen as a failure, the irony of calling it a “flop” is that the designers at Bell & Howell were onto something. The small screen system has since become the dominant model of in-flight entertainment, and the single-screen system has disappeared.</p>
<hr>
<h2>Going big – and going home</h2>
<p><strong>Thomas Delapa, University of Michigan</strong></p>
<p>Since the dawn of cinema, filmmakers have experimented with supersizing the screen and pushing the limits of what are called “aspect ratios,” or the ratio between the width and the height of the screen. </p>
<p>The 35mm motion picture standard dominated the silent-film era and survives even in our digital era. In classic Hollywood, this meant a square-ish projected frame: approximately 1.33 width ratio to 1 high. Rick and Ilsa in “Casablanca,” Scarlett and Rhett in “Gone With the Wind,” and Norma Desmond in “Sunset Boulevard” all played in the cozy virtual world of the 1.33 sandbox.</p>
<p>But film innovators eventually started looking for ways to go wider and bigger. There was French director Abel Gance’s three-screen <a href="https://books.google.com/books?id=HgcjMQAACAAJ&dq=Napoleon:+Abel+Gance's+classic+film&hl=en&sa=X&ved=0ahUKEwjKxfmq9MbZAhWWw4MKHU0RD9gQ6AEIJzAA">Polyvision</a> process for his 1927 epic “<a href="http://www.imdb.com/title/tt0018192/?ref_=nv_sr_7">Napoleon</a>.” There was RKO studio’s 70mm- wide “<a href="https://books.google.com/books?id=UXTAAgAAQBAJ&pg=PA134&lpg=PA134&dq=RKO+studio+%22natural+vision%22&source=bl&ots=K-m0lcuH34&sig=yCljZ9Bhm_AOeEU6gfa-OWT71eY&hl=en&sa=X&ved=0ahUKEwjknILc9MbZAhUn9YMKHVxXDMcQ6AEIOTAH#v=onepage&q=RKO%20studio%20%22natural%20vision%22&f=false">Natural Vision</a>” film gauge that made a brief appearance in the 1920s.</p>
<p>But of all the “before-their-time” widescreen inventions that popped and fizzled, few were as grandiose as <a href="http://www.widescreenmuseum.com/widescreen/70mm-feb1930.htm">the Grandeur process</a>, which was developed in the late 1920s. Utilizing a 70mm-wide film strip – twice the width of the standard 35mm – it was easily the most ambitious attempt of its time to make widescreen go mainstream in the U.S. </p>
<p>The Fox Film Corporation (what would become 20th Century Fox) was Grandeur’s primary sponsor. The technology premiered in New York City in September 1929, when Fox screened a program of newsreels that included a splashy tour of Niagara Falls. </p>
<p>Flashy entertainment followed in 1930’s “<a href="http://www.imdb.com/title/tt0020691/?ref_=nv_sr_1">The Big Trail</a>,” an epic Western starring a then-unknown former college football star who called himself John Wayne. In Fox’s gargantuan 6,000-seat Roxy Theatre in Manhattan, the Duke galloped across a 42-foot-wide-by-20-foot-tall screen, creating an enormous virtual vista that dwarfed those at most of the 1920s “picture palaces.”</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=286&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=286&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=286&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=359&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=359&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208175/original/file-20180227-36706-1tnjwe1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=359&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A still from ‘The Big Trail.’</span>
<span class="attribution"><a class="source" href="https://2.bp.blogspot.com/-ZjRNxt9B7s4/Vf8WQs2uJoI/AAAAAAAATLs/qWTGccCbsyI/s1600/the%2Bbig%2Btrail00016.png">21st Century Fox</a></span>
</figcaption>
</figure>
<p>Despite Grandeur’s gushing greatness, U.S. theater owners were less buoyant at the prospect of doubling down on new projectors and screens to accommodate its really big show. </p>
<p>Not only had Wall Street just infamously laid a gargantuan egg, but owners had just shelled out big-time money to convert to accommodate the “<a href="https://en.wikipedia.org/wiki/Sound_film#Triumph_of_the_%22talkies%22">talkies</a>” of the nascent sound era. Grandeur’s case wasn’t helped by the smallish box-office returns of “The Big Trail.”</p>
<p>Widescreen experimentation would largely disappear for the next two decades, only to be revived in the 1950s, which marked the beginning of big screen’s steroid era. Launched in 1953, <a href="https://www.academia.edu/4728298/CinemaScope_Selected_Documents_from_the_Spyros_P._Skouras_Archive">CinemaScope</a> nearly doubled the frame ratio to 2.35 to 1. Then there was the three-projector <a href="https://cinerama.com/History.aspx">Cinerama</a>, and a reprise of 70 mm filmmaking in Oscar-winning blockbusters like “<a href="http://www.imdb.com/title/tt0048960/?ref_=nv_sr_2">Around the World in 80 Days</a>.” </p>
<p>Grandeur’s main mistake was epically bad timing. In today’s evolving digital era, widescreen formats of varying sizes are de rigueur around the world – if not exactly grandeur.</p><img src="https://counter.theconversation.com/content/92496/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Sound, color and special effects transformed the moviegoing experience. These inventions decidedly did not.Leo Braudy, Leo S. Bing Chair in English and American Literature, USC Dornsife College of Letters, Arts and SciencesScott Higgins, Charles W. Fries Professor of Film Studies, Wesleyan UniversityStephen Groening, Assistant Professor of Cinema and Media Studies, University of WashingtonThomas Delapa, Lecturer, Department of Screen Arts & Culture, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/755632017-03-31T11:47:01Z2017-03-31T11:47:01ZThe Conversation quiz #5<figure><img src="https://images.theconversation.com/files/163447/original/image-20170331-31733-cbsbfa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">via shutterstock.com</span></span></figcaption></figure><p>Test how closely you’ve been reading The Conversation this week with these ten questions. </p>
<iframe id="quizWidget-390742" width="100%" height="700px" frameborder="0" border="none" src="https://www.boombox.com/widget/quiz/fi9xdWl6emVzLzM5MDc0Mg"></iframe><img src="https://counter.theconversation.com/content/75563/count.gif" alt="The Conversation" width="1" height="1" />
Ten questions. On your marks. Get set. Go.Gemma Ware, Head of AudioLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/485142015-10-05T05:29:36Z2015-10-05T05:29:36ZWhy does asparagus make some people’s pee smell but not others?<figure><img src="https://images.theconversation.com/files/97079/original/image-20151002-23109-90vok0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Have you eaten asparagus and noticed that it can alter how your urine smells? Perhaps you’ve heard about the phenomenon but wondered why it doesn’t seem to affect you. Or maybe you’ve eaten beetroot and then been worried there appeared to be blood in your water. Why do certain foods change our urine and does it make a difference to our health?</p>
<p>Observations of how what we eat can affect our pee can be traced back through history, from the ancient Greeks including <a href="http://dmd.aspetjournals.org/content/29/4/539.full">Antiphon and Theophrastes</a> to an early edition of the medical journal <a href="http://bit.ly/1N8s3b8">The Lancet in 1836</a>. But asparagus’s potential to affect urine was not formally described <a href="http://ota.ox.ac.uk/text/5174.html">until 1735</a>. This happened to coincide with the British agrarian revolution when fertilisers containing sulphur were first used on crops, although there is no real evidence to say if this effect is causal.</p>
<p>There have been different theories put forward over the years explaining why only some people notice a smell in their urine after eating asparagus. It was first thought that some people broke down the vegetable in a way that released a smelly chemical in the urine. In the UK, <a href="http://dmd.aspetjournals.org/content/29/4/539.full">data suggested</a> about half of the population were so-called “excretors” in this way. This led to a theory that the characteristic was carried by a dominant gene that only needed to be inherited from one parent.</p>
<p>Interestingly there have also been reports that women who are “non-excretors” can produce the odorous urine <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2125.1989.tb03432.x/pdf">when pregnant</a>. This suggested that any asparagus compound responsible for the smell could pass through the placenta and be converted to the smelly compound by the foetus that inherited the gene from their father.</p>
<h2>Odour or smell?</h2>
<p>The problem with the idea of a genetic ability to produce smelly urine is that there is not just one compound that always appears in urine after eating asparagus. Up to 29 different compounds from the vegetable are potential odourants, although methanethiol or methyl–mercaptin is the most predominant. The number of potential smelly molecules has given rise to an alternative theory, not that certain people don’t produce the chemicals but that some people lack the genetic ability to detect the smell.</p>
<p>One <a href="http://chemse.oxfordjournals.org/content/early/2010/09/27/chemse.bjq081.full">small study</a> asked 38 people to eat asparagus and then sniff their own and each other’s urine samples to see if they could detect unusual odours, and around 8% of participants did not produce detectable odourants. A further 6% reported not being able to smell the asparagus odour in any of the samples they were asked to sniff.</p>
<p>When looking at possible genetic causes, the researchers not find any particular genes associated with production of odorants. They did however, find that the ability to detect the smell was linked to a specific DNA sequence that varied between different people. This means a single molecule change in the genes responsible for smell may be linked to the inability to smell asparagus odour in urine.</p>
<p>The problem is that there aren’t actually that many studies of this phenomenon and most of those that have been carried out are small so evidence is limited. This means it’s hard to say whether “asparagus pee” is an ability to produce the compounds or smell them, or a bit of both.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/97080/original/image-20151002-23072-1m3ezr3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Blood red.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Asparagus has also been reported to change the colour of urine, giving it a greenish tinge, something that is also associated with beetroot. In some individuals, the potentially disturbing effect can be pink or red urine. This can lead to the false impression of blood appearing in the urine (haematuria).</p>
<p>Known as beeturia, the cause is not thought to be a genetic characteristic, but related to the physical state of the person who experiences it. The beetroot’s red pigments only appear in the urine if they are not damaged by the digestive process and are then absorbed and re-excreted by the kidneys. It is thought that <a href="http://chemse.oxfordjournals.org/content/early/2010/09/27/chemse.bjq081.abstract">this can happen</a> if the stomach is not acidic enough, or if the beetroot itself has high levels vitamin C in the beetroot itself. So, some people can produce beetroot-red urine some but not necessarily all of the time.</p>
<h2>Other foods</h2>
<p>Although asparagus and beetroot are the most commonly mentioned examples, it is actually likely that many foods have an effect on the chemicals that appear in urine. This allows doctors to use urine to assess a person’s <a href="http://ajcn.nutrition.org/content/93/2/314.short">dietary intake</a> by analysing the different chemicals it contains.</p>
<p>However, most changes aren’t usually noticeable even if they are associated with colour or smell changes. For example, coffee isn’t usually thought of as something that strongly effects urine but a recent study has shown that drinking two cups can be enough to lead to the presence of compounds such as vanillin which are often associated with a vanilla-like sweet smell.</p>
<p>Perhaps next time you visit the bathroom, you may be able to see or smell a chemical marker of what you have recently ate or drank. It is usually normal for metabolites from food to appear in urine, and should not be anything to be worried about. If however, you think there is blood or a distinct change you should always seek a medical opinion.</p><img src="https://counter.theconversation.com/content/48514/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Duane Mellor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The question of whether your reaction to asparagus is down to your stomach or your nose is a 300-year-old mystery.Duane Mellor, Assistant Professor in Dietetics, University of NottinghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/392172015-04-06T10:15:36Z2015-04-06T10:15:36ZSkunk cabbage blooms are a stinky herald of spring<figure><img src="https://images.theconversation.com/files/77051/original/image-20150403-9324-1tp1j08.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Too bad this picture's not scratch n sniff.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/slack12/483165151">slack12</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>I love the smell of skunk in early spring. That sulfur smell tells me that the snow is melting, the sun is rising higher into the sky, and soon a carpet of wildflowers will paint the forest floor in white, purple and pink.</p>
<p>But it’s not the stink of an unfortunate nocturnal road-crosser. It’s a flower. In fact, it is the earliest flower to bloom in the first days of spring – if not the last weeks of winter.</p>
<p>I’m a professor of plant biology. Every spring I take my students on a walk through the woods. While they’re off taking pictures of buttercups and lilies, I’m ankle deep in mud, looking for my favorite spring wildflower: <a href="http://plants.usda.gov/core/profile?symbol=SYFO">eastern skunk cabbage</a>, <em>Symplocarpus foetidus</em>. Its species name, “fetid flower,” is an understatement.</p>
<p>The philodendron, that beautiful sprawling houseplant, is a first cousin to skunk cabbage, as is the graceful and pleasantly scented peace lily. Here is the bad news: these plants are poisonous if you eat them. They’re all members of the plant family <a href="https://plants.usda.gov/java/ClassificationServlet?source=display&classid=Araceae">Araceae</a>, colloquially known as the Arums. Attractive, yes. Poisonous? Yes. This family of plants is infamous for its production of noxious <a href="https://doi.org/10.1146/annurev.arplant.56.032604.144106">calcium oxalate</a>. When <a href="http://emedicine.medscape.com/article/817016-overview">ingested</a> in high doses, this toxin can cause permanent liver damage. This is one cabbage you definitely don’t want to eat.</p>
<p>If you take a stroll through the late winter woods in the eastern half of North America from the midwest and mid-Atlantic states north, you might notice a few slushy spots where the snow has melted into circles. Look closer. In those circles you might see some thick leaves that only a botanist could love: cup-shaped, about the size of a softball, cresting above the snow. </p>
<p>The smell will be unmistakable. The flower is mottled purple and green, with a dull-colored spike in the middle. You’ve found it. That is skunk cabbage.</p>
<p>While all the other spring wildflowers are still in winter dormancy, skunk cabbage is springing to life. Equipped with a remarkable evolutionary trait, skunk cabbage can generate its own heat. It can melt the snow around it. Some skunk cabbage have been observed to generate warmth greater than room temperature, even on a chilly, snowy, late winter day.</p>
<p>The <a href="http://dx.doi.org/10.1104/pp.107.113563">biochemical explanation</a> of skunk cabbage’s ability to generate snow-melting heat is as elegant as it is simple. Within the skunk cabbages’ cells are mitochondria, the energy-generating machinery of all cells. In these mitochondria exists an enzyme called alternative oxidase, or AOX. This enzyme alters the energy-making capability of a cell. Instead of generating power for growth, it generates heat. These flowers can melt snow.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/77047/original/image-20150403-9345-9x2iiw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Skunk cabbage burning through the late winter ice.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/vasenka/5562227265">VasenkaPhotography</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>That’s how they can create those little snow clearings as they emerge in the spring. But why do they smell rotten? As the snow melts and flowers start to appear, there’s competition for pollinators. Some of the very first insects to emerge are beetles and flies. These guys thrive on decay. They’ve spent the winter months frozen, and are the first to rummage for food. </p>
<p>Many flowering plants, like skunk cabbage, <a href="http://lifeofplant.blogspot.com/2011/05/coevolution.html">co-evolved</a> with animals, primarily insects. The flower provides nourishment and the insect carries pollen from flower to flower. (You know, the birds and the bees spiel.) But why would a flower smell like decay? What type of animal would visit a malodorous flower?</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/77050/original/image-20150403-9332-kjzpxs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The alluring blossom, with its all important pollen.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/7147684@N03/2477928284">Jason Hollinger</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The skunk cabbage’s smell is a magnificent example of mimicry and defense. The stink deceives beetles and flies, fooling them into thinking that food is available. Instead of a smelly decaying animal carcass — their spring meal of choice — they’re tricked into visiting a flower filled with pollen, which they will then unintentionally carry to another flower. By mimicking the smell of decay, skunk cabbage has evolved the ability to exploit the first pollinators of the spring.</p>
<p>At the same time, the bitter taste and stink deter herbivores like deer and rabbits who would otherwise be happy to feast on these first leaves of spring.</p>
<p>Skunk cabbage, by any other name, would smell as fetid. But to me, it smells likes spring.</p><img src="https://counter.theconversation.com/content/39217/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>J Peter Coppinger does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>OK, it doesn’t smell great. But skunk cabbage has a unique secret weapon to help it be one of the first plants to emerge from the snow at the end of winter.J Peter Coppinger, Associate Professor of Biology, Rose-Hulman Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/384492015-03-06T15:35:22Z2015-03-06T15:35:22ZWarning: the truth behind handshake-sniffing may bum you out<figure><img src="https://images.theconversation.com/files/74065/original/image-20150306-13567-ew4klp.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">"Lovely day for it." "Woof yes!"</span> <span class="attribution"><span class="source">Craig Roberts</span></span></figcaption></figure><p>As we all know, a firm handshake is important in making a good first impression. It’s a sure sign of physical strength and, rightly or wrongly, we use it make all manner of judgements about character, personality and sincerity. </p>
<p>New research now suggests that we take away much more than this – quite literally – because shaking hands may also be a way that we smell each other. As you may have read elsewhere, an Israeli team <a href="http://elifesciences.org/content/4/e05154">published a paper</a> that showed that handshakes transfer aromatic compounds thought to be involved in social assessment – that is, making judgements about someone else by virtue of how they smell. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=711&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=711&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=711&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=893&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=893&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74067/original/image-20150306-13576-q66izv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=893&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">‘Don’t forget to sniff!’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/maplessinseattle/2618178183/in/photolist-6rUPaH-nbAu8Y-6GKPaX-5teuPz-3v2xfn-gJPzZF-nt8bww-34n5et-34n54H-4fQrFZ-faRfEy-mj7di2-4ZmRaa-bYZ5rC-6oyG29-dxGwon-7Sz7nr-b7o6We-8Fg7qb-6bu2ww-5vTqnK-8Jdzs-tFqQy-3v2wux-bz29nH-kQZnHF-oLV21-8RedFB-j66EQ-71ZMnt-obKUK9-q3YscJ-qsRDQY-bRDniD-57C55p-dm7ZQ1-cqt5oQ-6c5J5A-6nHZfS-8sQvn3-eifksN-b6Dae-7EAY63-9RFeHC-dq4Rih-nnzFRH-7VHu5X-5hDZim-hpEnDz-6FADUs">Isa Sorensen</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>They analysed the chemical compounds present on clean surgical gloves and those that had been worn during a single handshake with the bare hands of ten volunteers. A range of chemical compounds were transferred, including some involved in animal interactions or already known to occur in human skin secretions. </p>
<p>So handshakes transfer smelly compounds. And how often we smell our hands following a handshake depends on who we greet. By secretly filming 150 participants, the researchers found that both men and women spent more time smelling the hand they used in the handshake when they greeted someone of the same gender. When they greeted a member of the opposite sex, they spent more time smelling their non-shaking hand. </p>
<h2>Smell and social interaction</h2>
<p>These new results add to accumulating evidence that our sense of smell plays an important part in social interactions. We can detect whether someone is <a href="http://pss.sagepub.com/content/early/2014/01/21/0956797613515681.abstract">sick or healthy</a> through their body odour, or whether they are <a href="http://www.ncbi.nlm.nih.gov/pubmed/12011790">fearful</a>, for example. Women place <a href="http://www.sciencedirect.com/science/article/pii/S0191886908002250">particular value on smell</a> when judging suitability of potential partners, and prefer armpit odour of men who, among other qualities, are more <a href="http://www.sciencedirect.com/science/article/pii/S0306453008002667">genetically compatible</a> or <a href="http://rsbl.royalsocietypublishing.org/content/1/3/256">socially dominant</a>.</p>
<p>In turn, men find women’s armpit odour more attractive when women are close to <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2006.01125.x/abstract">ovulation</a> and exposure to vulvar scents collected around ovulation increases their testosterone levels, suggesting that scent might <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809382/">prime men for competition</a> over a fertile woman. Interestingly, women respond to fertile odour in just the same way, suggesting they are also sensitive to smells of <a href="http://www.sciencedirect.com/science/article/pii/S1090513813000731">potential competitors</a>. </p>
<p>So what exactly might we be assessing when we check out hand odour, and what might we use that information for?</p>
<p>Smell is usually thought to be important in sex and attraction, so it was surprising that sniffing of the shaking hand increased the most after greeting someone of the same sex. The researchers suggested that this could be a way to assess the competition (though they admit they did not ask about sexual orientation of the participants). </p>
<p>That would not completely rule out using hands to sniff out potential partners. Reactions to smells can change depending on context, so perhaps people increase focus on the opposite sex in more socially relevant settings, or if they are single and searching for someone special.</p>
<h2>But it’s not about the hands</h2>
<p>One problem with all this is that it remains unclear whether there is some particular communicatory value in the smell of a hand. So far as we know, there are no special secretory glands that are unique to the hand – the compounds present on hands are likely to be much the same as those that occur on many other parts of the body.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74068/original/image-20150306-13579-c6xr0l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bad plan?</span>
<span class="attribution"><a class="source" href="http://theconversation.com/drafts/38449/edit#">okili77</a></span>
</figcaption>
</figure>
<p>Yet we do use our hands to touch other parts of our body which produce specific and localised odours, including our lips, hair and, of course, more intimate areas. The researchers did not provide evidence that these are the source of some of the transferred smell compounds, but it seems plausible. Indeed, studies aiming to promote handwashing report all kinds of bodily traces, <a href="http://www.bbc.co.uk/news/magazine-19834975">including faecal bacteria</a>, on hands of ordinary people on the street.</p>
<p>This could provide the key to understanding hand-smelling. A simple handshake is a world away from the greeting ceremonies of other mammals. They are unconstrained by the social niceties of observing personal space and partake in abundant close-up sniffing, very often in the ano-genital area. </p>
<p>We simply don’t get to do this until we enter an intimate sexual relationship. But because hands wander, they pick up these more intimate odours and make them accessible in a socially acceptable way. In other words, offering a handshake could just be a polite and modern version of inviting someone to “sniff my butt”.</p><img src="https://counter.theconversation.com/content/38449/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>S Craig Roberts does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>After a handshake, we learned this week that we sniff our hands. But why? Hand smells are not all that interesting in themselves. This points to possibilities that you might not want to hear.S Craig Roberts, Senior Lecturer in Psychology, University of StirlingLicensed as Creative Commons – attribution, no derivatives.