tag:theconversation.com,2011:/au/topics/saliva-10926/articlesSaliva – The Conversation2022-05-26T20:39:17Ztag:theconversation.com,2011:article/1821252022-05-26T20:39:17Z2022-05-26T20:39:17ZCan you use rapid antigen tests in children under 2 years old?<figure><img src="https://images.theconversation.com/files/460487/original/file-20220429-17-drojpg.jpg?ixlib=rb-1.1.0&rect=2%2C0%2C995%2C666&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/brown-teddy-bear-sitting-on-sofa-2106255734">Shutterstock</a></span></figcaption></figure><p>As we head into winter, you may have a sniffly child under two years old at home. Is it just a cold? Or could it be COVID?</p>
<p>You may be tempted to reach into the cupboard for a rapid antigen test to find out. But some manufacturers say their COVID tests aren’t suitable for children under two.</p>
<p>Can you use a test intended for adults or older children? How do you test a wriggling or grumpy small child anyway? We’re infection control and child health researchers. Here are our tips.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/coronavirus-or-just-a-common-cold-what-to-do-when-your-child-gets-sick-this-winter-140727">Coronavirus or just a common cold? What to do when your child gets sick this winter</a>
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<h2>Are there special tests for this age group?</h2>
<p>Of the 47 different rapid antigen tests <a href="https://www.tga.gov.au/covid-19-rapid-antigen-self-tests-are-approved-australia">authorised</a> for home use in Australia at the time of writing, most (57%) state they are not suitable for children under two. This leaves 20 tests that are.</p>
<p>You can <a href="https://www.tga.gov.au/covid-19-rapid-antigen-self-tests-are-approved-australia">check the list</a> on the Therapeutic Goods Administration (TGA) website to see if the test you have at home is one of them.</p>
<p>Just because a test isn’t approved for a particular age doesn’t necessarily mean it doesn’t work at all. It usually means the test has not been tested, or its use determined, for that age. But try to use a test approved for under twos if you can.</p>
<p>However, rapid antigen tests are generally not as accurate in children as they are in adults. They are: </p>
<ul>
<li><p><strong>highly specific</strong> – rapid antigen tests for children have <a href="https://ebm.bmj.com/content/early/2022/01/04/bmjebm-2021-111828">high specificity</a>. This means if the test is done correctly, it is unlikely to say your child is positive if it is not </p></li>
<li><p><strong>but not as sensitive</strong> – rapid antigen tests are less sensitive in children than adults. In other words, they’re not as good at detecting if a child has COVID. But tests are <a href="https://ebm.bmj.com/content/early/2022/01/04/bmjebm-2021-111828">more likely</a> to correctly detect COVID if the child has symptoms.</p></li>
</ul>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/15-things-not-to-do-when-using-a-rapid-antigen-test-from-storing-in-the-freezer-to-sampling-snot-176364">15 things not to do when using a rapid antigen test, from storing in the freezer to sampling snot</a>
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<h2>Which type of test to use?</h2>
<p>Of the 20 tests approved for use in under twos, 16 use nasal swabs and four sample saliva. </p>
<p>The accuracy of different sampling methods in children differs by viral variant. While it was once thought nasal swabs were <a href="https://journals.lww.com/pidj/fulltext/2020/09000/nasal_swab_as_preferred_clinical_specimen_for.33.aspx">more accurate</a> in children, this may not necessarily be the case with the Omicron variant.</p>
<p>There’s <a href="https://www.medrxiv.org/content/10.1101/2021.12.22.21268246v1">preliminary evidence</a>, which has yet to be independently verified, saliva swabs may be better able to detect Omicron. So we’ll see how the evidence develops.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Rapid antigen test components with nasal swab" src="https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462928/original/file-20220513-18-gc9eud.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">Tests that use nasal swabs may be more accurate. But that may depend on the viral variant.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/covid19-nasal-swab-test-kits-saracov2-2027424992">Shutterstock</a></span>
</figcaption>
</figure>
<p>Taking a saliva sample may not be as straightforward as you think. </p>
<p>Depending on the test, your child may need to cough (several times, on demand) and spit into a tube. Or after you swab your child’s tongue and mouth, your child will need to keep the spongy tip of the swab in their mouth for a few minutes, without sucking or biting it. So getting an under two-year-old to cooperate is unlikely.</p>
<p>If you do go down this route you can use a <a href="https://www.rch.org.au/clinicalguide/guideline_index/COVID-19_swabbing/">tongue depressor</a> to flatten the tongue to take the sample. You can buy these from a pharmacy.</p>
<p>But with a bit of preparation (and an extra pair of hands) you should be able to use a nasal test on a young child. You should be able to do this without causing pain or distress, a <a href="https://www.rchpoll.org.au/polls/covid-19-testing-in-kids-what-concerns-parents/">common worry</a> for parents considering COVID testing their child.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-prepare-your-child-for-a-covid-test-165248">How to prepare your child for a COVID test</a>
</strong>
</em>
</p>
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<h2>How do I prepare?</h2>
<p>Understand what the <a href="https://www.rch.org.au/clinicalguide/guideline_index/COVID-19_swabbing/">COVID test</a> involves and plan to have the resources you need.</p>
<p>As you take the test components out of the packet, remember to keep them out of reach of your child. The chemicals can be toxic if swallowed, or can cause skin and eye irritation. Parents should also ensure small children don’t swallow test components, such as small bits of plastic.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Toddler holding security blanket in park or garden" src="https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=943&fit=crop&dpr=1 754w, https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=943&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/462932/original/file-20220513-13-onvo9u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=943&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Holding a favourite toy or blanket may help your child relax.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/toddler-boy-blue-eyes-overalls-outside-134286551">Shutterstock</a></span>
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<p>It’s also helpful to have two adults: one to perform the test and the other to hold and support the child.</p>
<p><a href="https://www.rch.org.au/kidsinfo/fact_sheets/Reduce_childrens_discomfort_during_tests_and_procedures/">Distraction</a> helps take your child’s mind off the test by concentrating on something more pleasurable. Young children can be easily distracted by listening to a favourite song. So have a song ready on your phone.</p>
<p>For toddlers, it can help to have another adult to provide more engaging distraction such as watching a video on a phone or tablet, or switching on a light-up toy.</p>
<p>Holding a favourite toy or blanket may also help your child relax. </p>
<h2>How do I actually take the sample?</h2>
<p>One adult can use a <a href="https://www.rch.org.au/clinicalguide/guideline_index/COVID-19_swabbing/">secure hugging hold</a> to reduce movement during the test while the other adult takes the sample. </p>
<p>The adult holding the child sits the child upright on their lap and holds them close to make them feel secure. They cross one arm across the child’s body and place the other hand on the child’s forehead.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sleeping baby wrapped tightly in checked blanket" src="https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/464418/original/file-20220520-13-ke69da.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Wrapping in a blanket can help.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/newborn-baby-boy-tightly-wrapped-blue-1142319218">Shutterstock</a></span>
</figcaption>
</figure>
<p>If you’re testing the child by yourself, you can wrap them in a blanket to hold them still while you take the sample. </p>
<p><a href="https://www.childrens.health.qld.gov.au/chq/information-for-families/helping-your-child-through-a-procedure/">Staying calm</a> yourself communicates to your child they are safe. Maintain a steady voice and breathe calmly during the test. </p>
<p>Slowly insert the tip of the swab inside the nose <a href="https://www.rch.org.au/clinicalguide/guideline_index/COVID-19_swabbing/">for about 1cm</a> or until you meet resistance. Angle it along the base of the inside of the nose horizontally rather than pointing it upwards as you insert it (<a href="https://www.rch.org.au/clinicalguide/guideline_index/COVID-19_swabbing/">go low</a>). </p>
<p>There is at least one nasal test that provides a smaller swab for young children so <a href="https://www.tga.gov.au/covid-19-rapid-antigen-self-tests-are-approved-australia">check the TGA site</a> if you wish to use it. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/go-low-go-slow-how-to-rapid-antigen-test-your-kid-for-covid-as-school-returns-175615">Go low, go slow: how to rapid antigen test your kid for COVID as school returns</a>
</strong>
</em>
</p>
<hr>
<h2>What do I do next?</h2>
<p>Children’s <a href="https://journals.lww.com/pain/Fulltext/2015/01000/Remembering_the_pain_of_childhood__applying_a.6.aspx">memories of medical tests</a> can influence how they respond next time. So, as your young child may need another rapid antigen test in the future, finish on a positive note. </p>
<p>Play with your child after the test and provide positive reinforcement. Give your toddler a simple reward, such as a stamp or sticker. </p>
<p>If the test is unsuccessful, give your child a chance to recover before trying again.</p>
<p>However, if you feel anxious about performing the test, or repeating it, seek the support of a health professional. Every test should be the best possible experience for your child to avoid unnecessary distress.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/covid-19-in-babies-heres-what-to-expect-181940">COVID-19 in babies – here's what to expect</a>
</strong>
</em>
</p>
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<img src="https://counter.theconversation.com/content/182125/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thea van de Mortel teaches into the Graduate Infection Prevention and Control program at Griffith University. </span></em></p><p class="fine-print"><em><span>Karin Plummer 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>Can you use a test intended for adults or older children? How do you test a wriggling or grumpy small child anyway? We’re infection control and child health researchers. Here are our tips.Thea van de Mortel, Professor, Nursing and Deputy Head (Learning & Teaching), School of Nursing and Midwifery, Griffith UniversityKarin Plummer, Research Fellow, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1589542022-02-16T18:55:54Z2022-02-16T18:55:54ZDrooling is a common symptom of Parkinson’s. Could a workout for the swallowing muscles help?<figure><img src="https://images.theconversation.com/files/444450/original/file-20220203-17-taxqxf.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5966%2C3968&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>Imagine not wanting to leave your house because of fear you would drool. That’s the choice many people with Parkinson’s disease confront every day.</p>
<p>Parkinson’s disease is the second most common neurodegenerative condition in Australia after dementia. It’s estimated around <a href="https://www.parkinsonsvic.org.au/images/site/publications/Research/Living_with_Parkinsons_Disease.pdf">70,000 Australians</a> live with it and one of the most vexing symptoms is drooling. People with Parkinson’s don’t produce more saliva. Rather, they don’t swallow their saliva as often or as well. </p>
<p>This debilitating symptom is experienced by up to <a href="https://pubmed.ncbi.nlm.nih.gov/19288042/">74% of people</a> who have Parkinson’s. Consequently, many avoid social situations and become socially isolated.</p>
<p>My team from <a href="https://parkc.co/">ParkC</a>, Curtin University, and Royal Perth Bentley Group, recently trialled a behavioural treatment called “expiratory muscle strength training” to see if it could help people with Parkinson’s who drool.</p>
<p>Our small <a href="https://www.doi.org/10.1007/s00455-022-10408-6">study</a>, published in the journal Dysphagia, has shown promising results.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/parkinsons-disease-blood-changes-may-occur-years-before-diagnosis-156060">Parkinson's disease: blood changes may occur years before diagnosis</a>
</strong>
</em>
</p>
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<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&rect=0%2C24%2C5472%2C3612&q=45&auto=format&w=1000&fit=clip"><img alt="An older woman sits on a couch and looks a little bit sad." src="https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&rect=0%2C24%2C5472%2C3612&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/394960/original/file-20210414-20-ugob4a.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">People with Parkinson’s don’t produce more saliva. Rather, they don’t swallow their saliva as often or as well.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>What is expiratory muscle strength training?</h2>
<p>Expiratory muscle strength training was first developed for <a href="https://www.sciencedirect.com/science/article/pii/S089219970200125X?casa_token=2Tix8SUoPfwAAAAA:UnF4xcFaYzeGMk0YEpaFy2BWO9nrO8yZ73_SD83bhXH7dgggJFtmfV61-A9-iiBxc0JOdu7ENhz7">high school band students</a> to increase exhalation strength.</p>
<p>It involves people blowing into a device against resistance. It’s a bit like blowing into a large straw but instead of the breath passing freely through the straw, the air encounters resistance. You find you have to blow harder, which helps strengthen the target muscles. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/403519/original/file-20210531-23-ffvq7j.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">Expiratory muscle strength training involves people blowing into a device against resistance.</span>
<span class="attribution"><span class="source">Naomi Cocks</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Just like a gym workout, people repeat this action multiple times and do this training five times a week. </p>
<p>Since its development, some <a href="https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=%22Expiratory+muscle+strength+training%22+parkinson%27s&btnG=">studies</a> by other researchers have found this training not only increases exhalation strength but also improves cough strength and the swallow. Problems with coughing and swallowing are difficulties often experienced by people with Parkinson’s. </p>
<p>We were interested to know whether this training also resulted in improvements in drooling.</p>
<h2>What we did</h2>
<p>Our study involved 16 people with Parkinson’s who had self-reported difficulties with drooling.</p>
<p>First, we wanted to make sure measures of their swallowing ability, cough strength, lip strength and self-reported drooling severity stayed stable over the space of one to two weeks.</p>
<p>If they did, we could be more confident any improvements seen after the therapy would be actually due to the therapy and not just instability in these measures.</p>
<p>Typically, participants in our study completed 30 sessions of expiratory muscle strength training over a six week period. </p>
<p>Training consisted of two sessions with a speech pathologist and three sessions at home alone.</p>
<p>After training, we again measured their swallowing ability, cough strength, lip strength and drooling. We found swallowing ability, cough strength and drooling all improved significantly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/403269/original/file-20210528-21-1nswrcr.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">People with Parkinson’s sometimes struggle with swallowing.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>The next step: a bigger study</h2>
<p>Our study was small and further research is clearly needed. But our promising preliminary results suggest this treatment may be a more desirable option than the standard approach to reduce drooling for people with Parkinson’s (botox shots, which reduce saliva production but can leave people with a dry mouth and difficulty swallowing).</p>
<p>One of the potential benefits of this treatment is that this single treatment could treat three difficulties common in Parkinson’s – drooling, swallowing and cough strength – all at the same time. </p>
<p>Difficulties swallowing and a weak cough can result in the person being at increased risk of developing pneumonia or choking. So not only could this treatment potentially reduce drooling, but also reduce the risk of serious illness and hospitalisation. </p>
<p>We are now seeking funding in order to explore this treatment’s efficacy with a greater number of participants in a randomised control trial. We hope our research will help people with Parkinson’s feel more comfortable with leaving their homes and, in doing so, improve their quality of life.</p>
<p><em>Please note: expiratory muscle strength training should not be carried out without consultation with a speech pathologist.</em></p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/parkinsons-disease-can-affect-the-eyes-heres-what-we-know-so-far-146432">Parkinson's disease can affect the eyes – here's what we know so far</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/158954/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Naomi Cocks has received funding from Parkinson’s WA.</span></em></p>The treatment is called ‘expiratory muscle strength training’; it is an exercise program targeting the muscles used when you swallow or cough.Naomi Cocks, Senior Lecturer, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1685492021-11-08T13:43:51Z2021-11-08T13:43:51ZDo flies really throw up on your food when they land on it?<figure><img src="https://images.theconversation.com/files/423207/original/file-20210925-14-1yipuw9.jpg?ixlib=rb-1.1.0&rect=115%2C121%2C3765%2C2445&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A fly regurgitating digestive juices.</span> <span class="attribution"><span class="source">Carlos Ruiz</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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<span class="caption"></span>
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</figure>
<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>Do flies really throw up on my food when they land on it? – Henry E., age 10, Somerville, Massachusetts</strong></p>
</blockquote>
<hr>
<p>Imagine you’re at a picnic and just about to bite into your sandwich. Suddenly you spot a fly headed your way, homing in on your food with help from its <a href="https://askentomologists.com/2015/02/25/through-the-compound-eye/">compound eyes</a> and antennae. It manages to escape your swatting, lands on the sandwich and then seems to throw up on it!</p>
<p>It can look kind of gross, but the fly might be just airing out its own digested food, or <a href="https://doi.org/10.1093/aesa/90.2.184">spitting on yours</a>.</p>
<p>Most of the <a href="https://www.si.edu/spotlight/buginfo/true-flies-diptera">over 110,000</a> known fly species <a href="https://doi.org/10.1673/031.008.7301">have no teeth</a>, so they cannot chew solid food. Their mouthparts are like a spongy straw. Once they land on your food, they need to release digestive juices to liquefy it into a predigested, slurpable soup they can swallow. In short, some flies are on a <a href="https://doi.org/10.1673/031.008.7301">liquid diet</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/N23E4jYTExk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A fly slurping its liquid meal.</span></figcaption>
</figure>
<p>To fit more food in their stomachs, some flies try to reduce the liquid in what they have already eaten. They regurgitate food into vomit bubbles to dry it out a bit. Once <a href="https://doi.org/10.1111/j.1365-3032.1992.tb01193.x">some water has evaporated</a> they can ingest this more concentrated food. </p>
<p>Human beings don’t need to do all this spitting and regurgitating to get nutrients out of our food. But you do produce a digestive juice in your saliva, an enzyme called <a href="https://1md.org/health-guide/digestive/ingredients/alpha-amylase">amylase</a>, which predigests some of the sandwich bread while you chew. Amylase breaks down starch, which you can’t taste, into simple sugars like glucose, which you can taste. That’s why <a href="https://doi.org/10.1093/chemse/bjz010">bread gets sweeter</a> the longer you chew it. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="closeup of a reddish insect with bristly black hairs on its body" src="https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=459&fit=crop&dpr=1 600w, https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=459&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=459&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=577&fit=crop&dpr=1 754w, https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=577&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/423212/original/file-20210925-23-18a0vfd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=577&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bristles and hair on a Tachinid fly.</span>
<span class="attribution"><span class="source">Maria Cleopatra Pimienta</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Did you know flies can taste food without their mouths? As soon as they land, they use receptors on their feet to decide whether they’re on something nutritious. You may have noticed a fly rubbing its legs together, like a hungry customer getting ready to devour a meal. <a href="https://doi.org/10.1016/j.cub.2020.01.045">This is called grooming</a> – the fly is essentially cleaning itself, and may also clean the <a href="https://doi.org/10.1016/j.conb.2009.07.001">taste sensors</a> on the <a href="https://doi.org/10.1523/JNEUROSCI.0649-14.2014">bristles and fine hair of its feet</a>, to get a better idea of what is in the food it has landed on.</p>
<h2>Should you trash food a fly’s landed on?</h2>
<p>When a fly touches down on your sandwich, that’s probably not the only thing it’s landed on that day. Flies often sit on gross stuff, like a dumpster or decomposing food, that’s full of microbes. The germs can hitch a ride and, if the fly stays put long enough, hop onto your meal. This is much more dangerous than their saliva because <a href="https://doi.org/10.1038/s41598-017-16353-x">some of the microbes</a> can cause diseases, like <a href="https://doi.org/10.1016/j.vaccine.2019.07.078">cholera</a> and <a href="https://doi.org/10.1353/pbm.2006.0005">typhoid</a>. But if the fly doesn’t stay longer than a few seconds the <a href="https://theconversation.com/should-i-throw-away-food-once-a-fly-has-landed-on-it-50895">chances of microbes transferring are low</a>, and your food is probably fine. </p>
<p>To keep insects from landing on your food, you should always cover it. If your house is infested with flies, you can use <a href="https://theconversation.com/how-to-kill-fruit-flies-according-to-a-scientist-81740">simple traps</a> to get rid of them. Carnivorous plants can also eat the flies and help control their population.</p>
<h2>Are flies good for anything?</h2>
<p>Spitting on food and spreading diseases sounds disgusting, but flies aren’t all bad. </p>
<p>Watch closely the next time you’re outside and you might be surprised by how many flies visit flowers to get nectar. They’re an important group of <a href="https://doi.org/10.3390/insects11060341">pollinators</a>, and many plants need flies to <a href="https://theconversation.com/tiny-cacao-flowers-and-fickle-midges-are-part-of-a-pollination-puzzle-that-limits-chocolate-production-154334">help them reproduce</a>.</p>
<p>Flies are also a good source of food for frogs, lizards, spiders and birds, so they’re a valuable <a href="https://doi.org/10.1002/ps.5807">part of the ecosystem</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="doctor working on patient's foot in background, tubes of maggots in foreground" src="https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429602/original/file-20211101-25-1rfhnd6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A doctor uses sterile maggots like those in these tubes to clean a patient’s foot wound.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/steril-gezüchtete-maden-im-vordergrund-in-reagenzgläsern-zu-news-photo/1213178783">Norbert Försterling/picture alliance via Getty Images</a></span>
</figcaption>
</figure>
<p>Some <a href="https://doi.org/10.1134/S0013873819030023">flies have medical uses</a>, too. For example, doctors use blow fly maggots – the young, immature form of flies – to remove decomposing tissue in wounds. The maggots release antiviral and antimicrobial juices, and these have helped scientists create new treatments for infections.</p>
<p>More importantly, the fruit flies you may have seen flying around ripe bananas in your kitchen have been <a href="https://theconversation.com/ode-to-the-fruit-fly-tiny-lab-subject-crucial-to-basic-research-38465">invaluable in biological research</a>. Biomedical scientists from all over the world study fruit flies to find <a href="https://doi.org/10.1016/S1369-7021(11)70113-4">causes and cures for diseases and genetic disorders</a>. And in <a href="https://faculty.fiu.edu/%7Etheobald/people/">our lab</a>, we study what the world looks like to insects, and how they use their vision to fly. This knowledge can inspire engineers to build better robots.</p>
<p>So, although it’s a nuisance to shoo flies away from your sandwich, maybe you can spare a few bits of your lunch?</p>
<hr>
<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/168549/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Theobald receives funding from the National Science Foundation: IOS-1750833. </span></em></p><p class="fine-print"><em><span>Ravindra Palavalli-Nettimi 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 fly does some of its digesting outside its body before it even eats any food.Ravindra Palavalli-Nettimi, Postdoctoral Research Associate, Florida International UniversityJamie Theobald, Associate Professor of Biological Sciences, Florida International UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1321722021-05-18T12:24:17Z2021-05-18T12:24:17ZThe truth about tooth decay<figure><img src="https://images.theconversation.com/files/353199/original/file-20200817-22-2742m2.jpg?ixlib=rb-1.1.0&rect=65%2C45%2C4314%2C2804&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The health of your teeth has a major effect on your body.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/MjO2ZWzPLtc">Rudy Fargo/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>To “cry poor mouth” is an expression used to habitually complain about a lack of money. A literal poor mouth, however, represents one of the most widespread global diseases: tooth decay. Cavities resulting from poor oral health can drive everything from <a href="https://doi.org/10.1177/2158244017728319">emotional issues</a> to low self-esteem and health concerns. </p>
<p>Even more critical is the socioeconomic impact of tooth decay. Cavities are a “hidden cost” across a person’s lifespan. They can affect the ability of children to learn, result in absenteeism and a loss of productivity for employees and employers, and <a href="https://dentistry.uic.edu/news-stories/the-many-costs-financial-and-well-being-of-poor-oral-health/">increase health costs for retirees</a>.</p>
<p>Untreated tooth decay can result in health complications including poor nutrition, if it is painful to chew; severe pain; and a higher risk of <a href="https://www.health.harvard.edu/staying-healthy/hidden-dental-dangers-that-may-threaten-your-whole-body">drug abuse and heart disease</a>, including an infection of the heart called <a href="https://www.doi.org/10.1080/20002297.2020.1768342">subacute bacterial endocarditis</a>. This heart condition, caused primarily by <em>Streptococcal</em> bacteria normally found in the mouth, can increase with tooth decay, move into the bloodstream and infect the heart valves, leading to loss of function and, while quite rare, can even lead to death. More recently, reports have documented that untreated dental cavities can result in <a href="https://www.theguardian.com/inequality/2017/jun/13/healthcare-gap-how-can-a-child-die-of-toothache-in-the-us">brain infections and death</a>. </p>
<p>What can you do to safeguard your teeth from decay? Are cavities inevitable? Does your genetic makeup determine how you are able to fend off decay? The answers, as you might guess, are complex. </p>
<h2>Who is at risk from tooth decay?</h2>
<p><a href="https://www.cdc.gov/nchs/products/databriefs/db191.htm">National data show</a> that more than 45% of children ages 2-19 have cavities, and nearly 17% of them go untreated. For adults, 92% of people ages 20-64 have experienced tooth decay, with more than 30% of these cavities left untreated. <a href="https://www.nidcr.nih.gov/research/data-statistics/dental-caries">These statistics</a> can be attributed to several intersecting factors. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A magenta toothbrush with neon-green bristles." src="https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/353236/original/file-20200817-22-1brzp3u.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 humble toothbrush can promote tooth health.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/MjO2ZWzPLtc">Pawel Czerwinski/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>First, some people believe that cavities are not a big deal and <a href="https://www.gilbreathdental.com/blog?p=is-tooth-loss-inevitable">losing teeth from decay is inevitable</a>. Second, <a href="https://www.whydental.org/about/industry-overview">dental insurance</a> is not widely offered with health insurance, and, while not overly expensive to purchase, more than 60% of the cost of dental procedures is not covered and has to be paid by an individual.</p>
<p>The exception is children on Medicaid, which generally covers the cost of dental treatments. However, Medicaid and Medicare have very limited coverage for dental procedures for adults and vary tremendously from state to state. </p>
<p>Finally, there continues to be a challenge in access to care that includes a <a href="https://www.dentistrytoday.com/news/industrynews/item/7336-the-united-states-needs-10-716-more-dentists-to-cover-shortage-areas">national lack of dentists</a>, uneven distribution of dentists in counties and states and particularly rural areas, substantial out-of-pocket costs and the critical role patients plan in maintaining good oral health. </p>
<figure class="align-right ">
<img alt="A man with beautiful white teeth smiling broadly." src="https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/353246/original/file-20200817-20-vnglz3.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">
<figcaption>
<span class="caption">A set of pearly whites can be an emotional asset.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/0pOlBhSsF80">Marcos Paulo Prado/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>A recipe for cavities</h2>
<p>There are four underlying biological features of cavities, beginning with the microbiome or the bacteria that live in the mouth. What a person eats also matters: How much and how often someone eats carbohydrates will determine how much acid will be created, since acid in the mouth dissolves the enamel covering that protects the teeth. The chemistry of saliva that bathes the oral cavity and protects teeth against cavities is another important aspect of health. And finally, genetics contribute to the structural characteristics of teeth and the ability to withstand tooth decay.</p>
<p>Since the initial reports were published in 2008 from the <a href="https://www.hmpdacc.org/">Human Microbiome Project</a>, supported by the National Institutes of Health, much has been learned about health and disease in relation to the microbiome of the mouth. One of the most important insights is the complex set of bacteria related to cavities, especially severe ones. Molecular microbiology studies have provided new evidence about the biology and ecology of tooth decay and the pathogens that have led to <a href="https://doi.org/10.1177/0022034517737024">new strategies and targets for therapeutics</a>. </p>
<h2>What causes decay?</h2>
<p>The bacteria or <a href="https://doi.org/10.1016/j.annepidem.2016.03.006">microbiome in families</a> has been shown to be related to cavities, the type of tooth, and their structure in the mouth. The bacteria of tooth decay colonize the oral cavity early in life and are transmitted from <a href="https://pubmed.ncbi.nlm.nih.gov/17036539/">mother to baby</a>. What may tip the balance into decay is diet, which plays a central part in how tooth decay is expressed. </p>
<p>Bacteria ferment a <a href="https://doi.org/10.1111/jcpe.12672">wide array of carbohydrates</a>, like sugar and high fructose corn syrup, to produce acid. This acid accumulates in the bacterial biofilms on the teeth, resulting in cavities. Acid-producing and acid-loving bacteria are the primary culprits in <a href="https://doi.org/10.1111/eos.12425">dissolving the enamel</a>, which protects the tooth. Once the enamel is dissolved, the underlying portion of the tooth, the dentin, is softer and more easily destroyed by the acid, thus leading to wider and deeper expansion of the cavity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Little boy holding up set of toy teeth." src="https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=470&fit=crop&dpr=1 600w, https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=470&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=470&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=590&fit=crop&dpr=1 754w, https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=590&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/353237/original/file-20200817-20-1w8ky1e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=590&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Teeth count for life.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/3O5GPcS3juY">Eddie Kopp/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To offset this corrosion, <a href="https://www.doi.org/10.1177/0022034517701902">recent therapeutics</a> containing acid buffering agents, such as <a href="https://www.doi.org/10.1177/0022034517735294">arginine</a>, are included in toothpastes and mouth rinses to <a href="https://doi.org/10.1177/0022034517735294">combat the disease</a>. Evidence also suggests that other dietary micronutrients, such as vitamin D, can lower the risk for cavities. These findings emphasize a better understanding of the biology of this global disease for improved prevention and treatment of cavities.</p>
<h2>The role of saliva</h2>
<p>It is estimated that one person swallows approximately a liter of saliva each day. The flow of saliva is substantially decreased while sleeping and is increased with eating or even when thinking about food. This <a href="https://DOI.org/10.1016/j.jdent.2004.10.009">mechanical cleansing</a> is critical for the health of the mouth. However, it is clear that “normal” saliva production and salivary flow varies across the population. Lower salivary flow is considered a risk for dental caries. </p>
<p>Importantly, internal and external factors can abnormally impact salivary flow. This can include radiation therapy, systemic diseases like <a href="https://doi.org/10.1007/s00784-015-1705-z">diabetes</a>, <a href="https://doi.org/10.1034/j.1600-051x.2000.027004231.x">autoimmune diseases</a> that affect the salivary glands, a wide array of <a href="https://doi.org/10.1007/s40268-016-0153-9">pharmaceuticals</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/18841733/">aging</a>. </p>
<p>New research firmly supports a <a href="https://doi.org/10.1016/j.archoralbio.2019.104522">genetic contribution</a> to the risk and development of cavities. The likely genetic influence is the characteristics of teeth and the ability of saliva to protect your mouth. It is clear that the microbiome in your mouth is critical in driving an environment where cavities can develop. </p>
<p>[<em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=youresmart">You can read us daily by subscribing to our newsletter</a>.]</p><img src="https://counter.theconversation.com/content/132172/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jeffrey Ebersole receives funding from the National Institutes of Health.</span></em></p>Cavity-free teeth depend on many factors, and heredity may not be the most important.Jeffrey Ebersole, Professor of Biomedical Sciences, University of Nevada, Las VegasLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1418772020-07-02T20:10:01Z2020-07-02T20:10:01ZExplainer: what’s the new coronavirus saliva test, and how does it work?<p>A cornerstone of containing the COVID-19 pandemic is widespread testing to identify cases and prevent new outbreaks emerging. This strategy is known as “test, trace and isolate”.</p>
<p>The standard test so far has been the swab test, in which a swab goes up your nose and to the back of your throat.</p>
<p>But an alternative method of specimen collection, using saliva, is being evaluated in Victoria and other parts of the world. It may have some benefits, even though it’s not as accurate.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/victoria-is-on-the-precipice-of-an-uncontrolled-coronavirus-outbreak-will-the-new-measures-work-141706">Victoria is on the precipice of an uncontrolled coronavirus outbreak. Will the new measures work?</a>
</strong>
</em>
</p>
<hr>
<h2>Saliva testing can reduce risks for health workers</h2>
<p>The gold standard for detecting SARS-CoV-2 (the coronavirus that causes COVID-19) is a polymerase chain reaction (PCR). This tests for the genetic material of the virus, and is performed most commonly on a swab taken from the nose and throat, or from sputum (mucus from the lungs) in unwell patients.</p>
<p>In Australia, more than 2.5 million of these tests have been carried out since the start of the pandemic, contributing significantly to the control of the virus.</p>
<p>Although a nasal and throat swab is the preferred specimen for detecting the virus, PCR testing on saliva has recently been <a href="https://theconversation.com/keep-your-nose-out-of-it-why-saliva-tests-could-offer-a-better-alternative-to-nasal-covid-19-swabs-138816">suggested</a> as an alternative method. Several studies demonstrate the feasibility of this approach, including one conducted at the <a href="https://jcm.asm.org/content/jcm/early/2020/04/17/JCM.00776-20.full.pdf">Doherty Institute</a> (where the lead author of this article works). It used the existing PCR test, but examined saliva instead of nasal samples.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/keep-your-nose-out-of-it-why-saliva-tests-could-offer-a-better-alternative-to-nasal-covid-19-swabs-138816">Keep your nose out of it: why saliva tests could offer a better alternative to nasal COVID-19 swabs</a>
</strong>
</em>
</p>
<hr>
<p>The use of saliva has several advantages:</p>
<ul>
<li><p>it is easier and less uncomfortable to take saliva than a swab</p></li>
<li><p>it may reduce the risk to health-care workers if they do not need to collect the sample</p></li>
<li><p>it reduces the consumption of personal protective equipment (PPE) and swabs. This is particularly important in settings where these might be in short supply.</p></li>
</ul>
<h2>But it’s not as sensitive</h2>
<p>However, a recent <a href="https://www.medrxiv.org/content/10.1101/2020.05.26.20112565v1">meta-analysis</a> (not yet peer-reviewed) has shown detection from saliva is less sensitive than a nasal swab, with a lower concentration of virus in saliva compared to swabs. It’s important to remember, though, this data is preliminary and must be treated with caution.</p>
<p>Nonetheless, this means saliva testing is likely to miss some cases of COVID-19. This was also shown in our <a href="https://jcm.asm.org/content/jcm/early/2020/04/17/JCM.00776-20.full.pdf">recent study</a>, which compared saliva and nasal swabs in more than 600 adults presenting to a COVID-19 screening clinic.</p>
<p>Of 39 people who tested positive via nasal swab, 87% were positive on saliva. The amount of virus was less in saliva than in the nasal swab. This most likely explains why testing saliva missed the virus in the other 13% of cases. </p>
<p>The laboratory test itself is the same as the PCR tests conducted on nasal swabs, just using saliva as an alternative specimen type. However, Australian laboratories operate under strict quality frameworks. To use saliva as a diagnostic specimen, each laboratory must verify saliva specimens are acceptably accurate when compared to swabs. This is done by testing a bank of known positive and negative saliva specimens and comparing the results with swabs taken from the same patients. </p>
<h2>When could saliva testing be used?</h2>
<p>In theory, there are several settings where saliva testing could play a role in the diagnosis of COVID-19. These may include:</p>
<ul>
<li><p>places with limited staff to collect swabs or where high numbers of tests are required</p></li>
<li><p>settings where swabs and PPE may be in critically short supply</p></li>
<li><p>some children and other people for whom a nasal swab is difficult. </p></li>
</ul>
<p>The use of saliva testing at a population level has not been done anywhere in the world. However, a pilot study is <a href="https://www.gov.uk/government/news/new-saliva-test-for-coronavirus-piloted-in-southampton">under way</a> in the United Kingdom to test 14,000 health workers. The US Food and Drug Administration recently issued an emergency approval <a href="https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-first-diagnostic-test-using-home-collection-saliva">for a diagnostic test</a> that involves home-collected saliva samples.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1276137829597396992"}"></div></p>
<p>In Australia, the Victorian government is also piloting the collection of saliva in <a href="https://www.dhhs.vic.gov.au/coronavirus-covid-19-daily-update">limited circumstances</a>, alongside traditional swabbing approaches. This is to evaluate whether saliva collection is a useful approach to further expanding the considerable swab-based community testing occurring in response to the current <a href="https://theconversation.com/victoria-locks-down-36-melbourne-suburbs-to-try-to-control-covid-19-spike-141707">outbreaks in Melbourne</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/these-10-postcodes-are-back-in-stage-3-coronavirus-lockdown-heres-what-that-means-141705">These 10 postcodes are back in Stage 3 coronavirus lockdown. Here's what that means</a>
</strong>
</em>
</p>
<hr>
<h2>A saliva test may be better than no test at all</h2>
<p>Undoubtedly, saliva testing is less sensitive than a nasal swab for COVID-19 detection. But in the midst of a public health crisis, there is a strong argument that, in some instances, a test with moderately reduced sensitivity is better than no test at all.</p>
<p>The use of laboratory testing in these huge volumes as a public health strategy has not been tried for previous infectious diseases outbreaks. This has required a scaling up of laboratory capacity far beyond its usual purpose of diagnosing infection for clinical care. In the current absence of a vaccine, widespread testing for COVID-19 is likely to occur for the foreseeable future, with periods of intense testing required to respond to local outbreaks that will inevitably arise. </p>
<p>In addition to swab-free specimens like saliva, testing innovations include self-collected swabs (which has <a href="https://www.medrxiv.org/content/10.1101/2020.04.09.20057901v1">also been tested in Australia</a>), and the use of <a href="https://www.livescience.com/pooled-testing-us-coronavirus.html">batch testing</a> of specimens. These approaches could complement established testing methods and may provide additional back-up for population-level screening to ensure testing is readily available to all who need it.</p>
<hr>
<p><em>This article is supported by the <a href="https://theconversation.com/au/partners/judith-neilson-institute">Judith Neilson Institute for Journalism and Ideas</a>.</em></p><img src="https://counter.theconversation.com/content/141877/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Deborah Williamson receives funding from the National Health and Medical Research Council. </span></em></p><p class="fine-print"><em><span>Allen Cheng receives funding from the National Health and Medical Research Council. He is a member of government advisory committees, including those involved in COVID-19 responses. </span></em></p><p class="fine-print"><em><span>Sharon Lewin receives funding from the National Health and Medical Research Council of Australia, the Medical Research Future Fund, the National Institutes of Health, the Wellcome Trust and the American Foundation for AIDS Research</span></em></p>Saliva testing is less sensitive than a nasal swab. But in the midst of a public health crisis, in some cases a test with slightly reduced sensitivity may be better than no test at all.Deborah Williamson, Professor of Microbiology, The Peter Doherty Institute for Infection and ImmunityAllen Cheng, Professor in Infectious Diseases Epidemiology, Monash UniversitySharon Lewin, Director, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne and Royal Melbourne Hospital and Consultant Physician, Department of Infectious Diseases, Alfred Hospital and Monash University, The Peter Doherty Institute for Infection and ImmunityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1388162020-05-19T20:01:42Z2020-05-19T20:01:42ZKeep your nose out of it: why saliva tests could offer a better alternative to nasal COVID-19 swabs<figure><img src="https://images.theconversation.com/files/335961/original/file-20200519-83363-hns6p8.jpg?ixlib=rb-1.1.0&rect=21%2C0%2C7160%2C4780&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>Saliva is one of our biggest foes in the COVID-19 pandemic, because of its role in spreading the virus. But it could be our friend too, because it potentially offers a way to diagnose the disease without using invasive nasal swabs.</p>
<p>Our research review, <a href="https://www.mdpi.com/2075-4418/10/5/290">published in the journal Diagnostics</a>, suggests saliva could offer a readily accessible diagnostic tool for detecting the presence of SARS-CoV-2, the virus that causes COVID-19, and might even be able to reveal whether someone’s immune system has already encountered it.</p>
<p>COVID-19 testing is a crucial part of the pandemic response, especially now countries are gradually lifting social distancing restrictions. This requires widespread, early, accurate and sensitive diagnosis of infected people, both with and without symptoms.</p>
<p>Our review looked at the results of three different studies, in Hong Kong, the nearby Chinese mainland city of Shenzhen, and Italy. All three studies found SARS-CoV-2 is indeed present in the saliva of COVID-19 patients (at rates of 87%, 91.6%, and 100% of patients, respectively). This suggests saliva is a potentially very useful source of specimens for detecting the virus.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-positives-and-negatives-of-mass-testing-for-coronavirus-137792">The positives and negatives of mass testing for coronavirus</a>
</strong>
</em>
</p>
<hr>
<p>Saliva <a href="https://www.sciencedirect.com/science/article/pii/S016041202031254X">spreads the SARS-CoV-2 virus</a> via breathing, coughing, sneezing, and <a href="https://www.nap.edu/catalog/25769/rapid-expert-consultation-on-the-possibility-of-bioaerosol-spread-of-sars-cov-2-for-the-covid-19-pandemic-april-1-2020">conversation</a>, which is why guidelines suggest we maintain a distance of at least 1.5 metres from one another. We also know <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7094991/">SARS-CoV-2 can survive in tiny droplets of saliva</a> in an experimental setting.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=242&fit=crop&dpr=1 600w, https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=242&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=242&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=305&fit=crop&dpr=1 754w, https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=305&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/335968/original/file-20200519-83388-16ad0ui.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=305&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="license">Author provided</span></span>
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<p>Saliva is an attractive option for detecting SARS-CoV-2, compared with the <a href="https://www.healthdirect.gov.au/coronavirus-covid-19-seeing-a-doctor-getting-tested-faqs#diagnosis">current tests</a> which involve taking swabs of mucus from the upper respiratory tract. Saliva is easy to access, which potentially makes the tests cheaper and less invasive. Saliva can hold up a <a href="https://www.ncbi.nlm.nih.gov/pubmed/19726214">mirror to our health</a>, not just of our mouth but our whole body. </p>
<p>For this reason, saliva has already been widely investigated as a diagnostic tool for chronic systemic diseases, as well as for oral ailments such as periodontal disease and oral cancers. But less attention has been given to its potential usefulness in acute infectious diseases such as COVID-19, perhaps because researchers and clinicians don’t yet appreciate its full potential. </p>
<h2>What a mouthful</h2>
<p>When we get sick, much of the evidence is present in our saliva – from the germs themselves, to the antibodies and immune system proteins we use to fight them off. Saliva also contains genetic material and other cellular components of pathogens after we have broken them down (for the full biochemical breakdown of the weird and wonderful things in our saliva, see pages 51-61 of our <a href="https://www.mdpi.com/2075-4418/10/5/290">review</a>).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=545&fit=crop&dpr=1 600w, https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=545&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=545&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=685&fit=crop&dpr=1 754w, https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=685&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/335967/original/file-20200519-83397-65o81d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=685&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="license">Author provided</span></span>
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</figure>
<p>Saliva is also hardy. It can be <a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=High-yield+RNA-extraction+method+for+saliva">stored at –80°C for several years with little degradation</a>.</p>
<p>This means it would be relatively straightforward to track the progression of COVID-19 in individual patients, by collecting saliva at various times during the disease and recovery. Saliva tests from recovered patients could also tell us if they have encountered the disease for a second time, and how strong their immune response is.</p>
<p>However, there is no research yet available on using saliva to monitor immune responses. This will be well worth investigating, given the pressing need for a reliable and cost-effective way to monitor the population for immunity to COVID-19 as the outbreak continues.</p>
<h2>Could saliva testing replace nasal swabs?</h2>
<p>An ideal saliva test would be a disposable, off-the-shelf device that could be used at home by individuals, without exposing them or others to the risk of visiting a clinic.</p>
<p>One drawback with the research so far is that it has involved small numbers of patients (each of the three studies we reviewed involved no more than 25 people), and there is little published detail on exactly how these studies collected the saliva – whether from the mouth or throat, whether by spitting, drooling or swabbing, and whether collected by the patient or by a clinician.</p>
<p>Nevertheless, based on the modest amount of research done so far, saliva looks like a promising candidate for COVID-19 testing. More research is now needed, in larger groups of people, to learn more about how to confidently test for SARS-CoV-2 in the saliva of both symptomatic and non-symptomatic people.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-do-we-make-saliva-130288">Curious Kids: why do we make saliva?</a>
</strong>
</em>
</p>
<hr>
<p>Earlier this month the US Food and Drug Administration <a href="https://www.nytimes.com/2020/05/08/health/fda-coronavirus-spit-test.html">approved the sale</a> of saliva-based COVID-19 test kits that will allow people to collect their own samples and send them to a lab for analysis.</p>
<p>A reliable test would offer a cheaper, less invasive and potentially even more accurate way to detect the virus, which would also reduce the risk posed by routine COVID-19 checks to both patients and front-line medical professionals.</p><img src="https://counter.theconversation.com/content/138816/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Pingping Han works on salivary diagnostic research at the University of Queensland. She is affiliated with the School of Dentistry, at The University of Queensland</span></em></p>The SARS-CoV-2 coronavirus is currently detected using invasive nasal swabs. But the virus is also present in saliva, potentially paving the way for cheaper, safer tests that people could do at home.Pingping Han, Postdoctoral Research Fellow, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1302882020-02-06T04:09:25Z2020-02-06T04:09:25ZCurious Kids: why do we make saliva?<figure><img src="https://images.theconversation.com/files/313858/original/file-20200206-149766-1wnt9we.jpg?ixlib=rb-1.1.0&rect=15%2C15%2C5160%2C3430&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">From shutterstock.com</span></span></figcaption></figure><blockquote>
<p><strong>Why do we make saliva? – Lilia, aged 7.</strong></p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>Thanks for your great question, Lilia. I’m a dentist, so I know a bit about what’s happening inside our mouths, and I can tell you saliva is very important.</p>
<p>It helps us enjoy our food, it helps sores in our mouth get better, and it fights nasty germs – just to name a few.</p>
<p>But first, let’s look at how we make saliva.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-do-tears-come-out-of-our-eyes-when-we-cry-84361">Curious Kids: Why do tears come out of our eyes when we cry?</a>
</strong>
</em>
</p>
<hr>
<h2>It comes from our salivary glands</h2>
<p><a href="https://www.mdpi.com/2073-4409/8/9/976">Saliva</a> is made in special pouches called salivary glands. These glands look like rows of water balloons that fill and empty into tubes called salivary ducts. As the balloon-like glands fill up, the saliva gets squeezed into the tubes, and then your mouth. </p>
<p>We have hundreds of little salivary glands dotted all around our lips and cheeks. We also have six big glands (made of hundreds of little glands) in our mouth that produce most of our saliva; four are under our tongue and one on each side of our cheeks.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/313864/original/file-20200206-149757-1yt15wg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">If you hold your bottom lip open, in less than a minute, you will notice tiny drops of liquid appearing. This saliva is made by your small salivary glands.</span>
<span class="attribution"><span class="source">From shutterstock.com</span></span>
</figcaption>
</figure>
<p>Everyone produces different amounts of saliva, depending on how healthy you are and how much water you drink. In one day, you could produce enough saliva to fill more than a litre carton of milk. In one year, you could make enough saliva to fill two bath tubs. That’s a lot of spit!</p>
<h2>Saliva’s super powers</h2>
<p>Our <a href="https://www.thejpd.org/article/S0022-3913(01)54032-9/fulltext">saliva</a> is mostly (99%) made of water, mixed with useful things like salts. </p>
<p>The ingredients in saliva are complicated, but that 1% is important. Saliva can help protect us against cavities (holes in the teeth) by washing our teeth with special salts. And because it’s slippery, saliva stops the bugs that create holes from sticking to our teeth.</p>
<p>If you have a cut inside your mouth or lose a baby tooth, saliva can help you heal faster. It can also fight most nasty germs and makes it difficult for bad bacteria (or bugs) to stick and grow in our mouth.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-tongues-taste-food-103744">Curious Kids: how do tongues taste food?</a>
</strong>
</em>
</p>
<hr>
<p>Saliva <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6855406/">helps you</a> enjoy the flavours in your food by helping your taste buds break food down into smaller bits. It also helps mash and mix food, so it’s easier to swallow and digest.</p>
<p>Saliva even helps you talk by making it slimy enough for your cheeks, lips and tongue to slip and slide around your mouth to form sounds.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/313893/original/file-20200206-149747-1lyq5zm.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">Saliva helps us enjoy and digest our food.</span>
<span class="attribution"><span class="source">From shutterstock.com</span></span>
</figcaption>
</figure>
<h2>How can you make more good saliva?</h2>
<p>Some people don’t make enough saliva because they may be sick or take medicine that stops their salivary glands from working well. </p>
<p>People who make very little saliva have trouble chewing and tasting their food, can get a lot of cuts and sores in their mouth, can be more likely to get holes in their teeth, and have other problems. </p>
<p>To help your salivary glands make a lot of good <a href="https://espace.library.uq.edu.au/view/UQ:326004">saliva</a>, you should make sure you drink plenty of water every day (at least one litre). Drink more water after playing sport, especially if you have sweated a lot. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-voices-come-out-of-our-mouths-130286">Curious Kids: how do voices come out of our mouths?</a>
</strong>
</em>
</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p><img src="https://counter.theconversation.com/content/130288/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arosha Weerakoon has received funding from Colgate for her research. She is a member of the Australian Dental Association as well as the International Association for Dental Research. She is a Fellow of the Royal Australasian College of Dental Surgeons.</span></em></p>Spit, drool, dribble, slaver, slobber or sputum – saliva has many different names. It also has many different jobs.Arosha Weerakoon, Lecturer, General Dentist & PhD Candidate, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1112502019-04-30T02:29:20Z2019-04-30T02:29:20ZExplainer: what is Sjögren’s syndrome, the condition Venus Williams lives with?<p>Sjögren’s syndrome hit the headlines when US tennis player Venus Williams declared she was <a href="https://www.theguardian.com/sport/blog/2017/jul/17/venus-williams-longevity-diet-wimbledon-tennis">suffering from it</a>.</p>
<p>What is Sjögren’s syndrome? How do you pronounce it anyway? And is there a cure?</p>
<h2>What is it?</h2>
<p><a href="https://www.mayoclinic.org/diseases-conditions/sjogrens-syndrome/symptoms-causes/syc-20353216">Sjögren’s syndrome</a>, pronounced “Showgren’s syndrome”, is what doctors call a chronic systemic autoimmune disease. It’s when the body’s immune system mistakenly attacks itself, leading to healthy tissues being destroyed. It’s chronic because it lasts for a long time, and systemic as it affects different organs.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-are-autoimmune-diseases-22577">Explainer: what are autoimmune diseases?</a>
</strong>
</em>
</p>
<hr>
<p>It can occur on its own, when it’s known as primary Sjögren’s syndrome, or with another autoimmune condition, such as lupus, rheumatoid arthritis, or systemic sclerosis, and is then called secondary or associated Sjögren’s syndrome. Like most autoimmune diseases, there is no cure.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-its-never-lupus-television-illness-and-the-making-of-a-meme-1198">Why 'It’s never lupus' - television, illness and the making of a meme</a>
</strong>
</em>
</p>
<hr>
<h2>What are the symptoms?</h2>
<p>The most common symptoms arise when immune cells (lymphocytes) attack the body’s own saliva and tear glands. This leads to the body producing fewer tears and less saliva (the so-called sicca syndrome).</p>
<p>Fewer tears leads to dry eyes (keratoconjunctivitis sicca), when the eyes feel gritty and like there’s something lodged there. Eyes also get tired after a lot of reading. Less saliva leads to a dry mouth (xerostomia). The mouth often feels uncomfortable or stings, and people have difficulty chewing and swallowing food.</p>
<p>These symptoms of dryness often also affect other parts of the body such as the nose, upper airways, vagina, and skin.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-the-immune-system-19240">Explainer: what is the immune system?</a>
</strong>
</em>
</p>
<hr>
<p>Fatigue, and muscle and joint pains occur in more than <a href="https://www.nejm.org/doi/full/10.1056/NEJMcp1702514?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed">80% of people</a> with the syndrome, leading to reduced quality of life.</p>
<p>In <a href="https://www.nejm.org/doi/full/10.1056/NEJMcp1702514?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed">30-40% of people</a> with primary Sjögren’s syndrome, other parts of the body are also affected, such as the skin, joints, brain, nerves, lymph nodes, kidneys, heart, and lungs. </p>
<p>There is also a risk of developing <a href="https://www.cancer.org/cancer/non-hodgkin-lymphoma/about/what-is-non-hodgkin-lymphoma.html">non‐Hodgkin lymphoma</a>, that is <a href="https://ard.bmj.com/content/73/6/1151">roughly 14 times higher than in the general population</a>.</p>
<h2>Who is affected?</h2>
<p>Sjögren’s syndrome is one of the most common autoimmune illnesses and the primary form affects about <a href="https://www.nejm.org/doi/full/10.1056/NEJMcp1702514?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed">0.3-1.0 per 1,000 people</a>. </p>
<p>According to the Australian Sjögren’s Syndrome Association website, <a href="http://www.sjogrens.org.au/">up to 0.5% of Australians have the condition</a>, considerably more than the international figures.</p>
<p>However, this figure needs to be confirmed in a prospective epidemiological study, which has yet to be done.</p>
<p>Setting up an Australian national registry would be useful in determining whether the syndrome really is more common in Australians, and for gaining clues about what might cause this condition.</p>
<p>Nine times as many women <a href="https://www.sciencedirect.com/science/article/pii/S1521694216300134?via%3Dihub">are affected</a> as men, and the syndrome is most common in 50-60 year-olds, although children and elderly people can also be affected.</p>
<h2>It’s tricky to diagnose</h2>
<p>This condition is as challenging to diagnose as it is to manage. General symptoms, such as unexplained fever, involuntary weight loss, pain, fatigue, and even dryness, are not specific to this illness, and can delay the diagnosis for years. </p>
<p>Inflammation of the muscles, joints, skin, nervous system, kidneys or lungs – which may lead to organ failure – can also mislead, as this can mimic other diseases such as rheumatoid arthritis, lupus or multiple sclerosis. </p>
<p>It is also important to distinguish primary Sjögren’s syndrome from non-autoimmune conditions such as perimenopause, endocrine disorders, or fibromyalgia, which do not require monitoring or treatment of organs affected by the condition. </p>
<p>Finally, defining whether it is a primary or secondary disease is not always easy.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/hidden-and-unexplained-feeling-the-pain-of-fibromyalgia-48319">Hidden and unexplained: feeling the pain of fibromyalgia</a>
</strong>
</em>
</p>
<hr>
<p>Primary Sjögren’s syndrome should be suspected in someone with dryness of the mouth and eyes, joint pain and/or fatigue, with or without symptoms of systemic (other organ) complications.</p>
<p>Your doctor will perform a detailed clinical examination, and run non-invasive tests to measure mouth and eye dryness, in consultation with a rheumatologist.</p>
<p>You will also have a specific blood test to confirm the autoimmune disease, and if that is not conclusive you may need a biopsy (a small sample) of the minor salivary gland. This is a minor dental procedure performed under local anaesthetic. It can confirm primary Sjögren’s syndrome and also exclude other diseases that mimic it and need different therapy. </p>
<p>Researchers are looking into whether using <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/1756-185X.13492">simple ultrasound techniques</a> can help with the difficult task of diagnosis.</p>
<h2>Can we treat it?</h2>
<p>As there is no cure, the best we can do is to manage the symptoms. But the few approved treatment options make this illness extremely challenging to manage. </p>
<p>Fatigue is difficult to treat. Other conditions that cause fatigue such as hypothyroidism and obstructive sleep apnoea need to be ruled out, and patients need to learn how to pace themselves within their limitations, while exercising and keeping as fit as possible.</p>
<p>Artificial tears (eye drops) help lubricate dry eyes and patients need to keep eyelids free from infection. For dental health, regular checkups and fluoride treatment are recommended, as are using sugar-free chewing gum or lozenges to stimulate saliva production.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/270340/original/file-20190423-15194-pi20d1.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">Special eye drops that mimic tears help to lubricate dry eyes.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/552942619?src=Ku4TgurtALlEVXcf1ebFwg-1-0&size=medium_jpg">from www.shutterstock.com</a></span>
</figcaption>
</figure>
<p>Chemical stimulation using <a href="https://pubchem.ncbi.nlm.nih.gov/compound/pilocarpine">pilocarpine</a> or <a href="https://www.drugbank.ca/drugs/DB00185">cevimeline</a> (the latter not available in Australia) can stimulate saliva and tear production. </p>
<p>Topical cyclosporine can also be used to treat eye dryness, under supervision of an ophthalmologist, and eye drops made from an extract of the patient’s blood can, in extreme cases, be useful. </p>
<p>Systemic (bodily) symptoms can be treated with glucocorticoids, hydroxychloroquine, or immunosuppressants such as mycophenolate mofetil, rituximab, cyclosporine, azathioprine, methotrexate or leflunomide.</p>
<p>However, none of these drugs used to treat the systemic symptoms have been proven to be effective in clinical trials in treating patients with primary Sjögren’s syndrome; their use is “off-label”, based on how we treat other autoimmune diseases such as lupus.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-why-are-off-label-medicines-prescribed-44783">Explainer: why are off-label medicines prescribed?</a>
</strong>
</em>
</p>
<hr>
<h2>Looking to the future</h2>
<p>Several new treatments for primary Sjögren’s syndrome are being trialled for their safety and efficacy. If approved, they will allow therapy to be tailored to the individual and should lead to an improved quality of life.</p>
<p>Their aim is to stop the progression of the disease, halt the autoimmune process, and help reduce the use of treatments with strong side-effects, such as glucocorticoids and immunosuppressants.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-how-do-drugs-get-from-the-point-of-discovery-to-the-pharmacy-shelf-78915">Explainer: how do drugs get from the point of discovery to the pharmacy shelf?</a>
</strong>
</em>
</p>
<hr>
<p>Drugs in trials or soon to be tested include:</p>
<ul>
<li><p>belimumab (promising results from a recent <a href="https://ard.bmj.com/content/74/3/526.long">phase 2 clinical trial</a>, which targets a molecule called <a href="https://www.nature.com/articles/nrrheum.2014.33">BAFF</a>, and which has recently been approved for use in people with lupus)</p></li>
<li><p>belimumab alone or with rituximab, in a new <a href="https://clinicaltrials.gov/ct2/show/NCT02631538">phase 2 clinical trial</a>, and</p></li>
<li><p>several other biological agents that target different steps in the body’s immune response, largely by interfering with the work of key enzymes or receptors.</p></li>
</ul>
<p>Without knowing the precise symptoms Venus Williams lives with, her success and achievements – <a href="http://www.tennis.com/player/406/venus-williams/">still competing with the world’s best tennis players</a> at the age of 38 – is more than impressive. Her fighting spirit, always with a positive attitude, drives hope for other people with Sjögren’s syndrome.</p><img src="https://counter.theconversation.com/content/111250/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Fabien B. Vincent receives funding from the Rebecca L. Cooper Medical Research Foundation. </span></em></p><p class="fine-print"><em><span>Maureen Rischmueller receives funding for consultancy from BMS, CSL and Behring, and for clinical Trials from BMS.</span></em></p>Sjögren’s syndrome has no cure. Here’s how it affects the body and what the future might bring for people with this challenging autoimmune disease.Fabien B. Vincent, Research Fellow; Rheumatology Research Group, Centre for Inflammatory Diseases, Monash UniversityMaureen Rischmueller, Rheumatologist and Associate Professor, Discipline of Medicine, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/720642017-02-01T00:02:26Z2017-02-01T00:02:26ZThe frog tongue is a high-speed adhesive<figure><img src="https://images.theconversation.com/files/154678/original/image-20170130-7894-20l6t5.jpg?ixlib=rb-1.1.0&rect=5%2C410%2C3384%2C2273&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Gotcha, five times faster than the blink of an eye. </span> <span class="attribution"><span class="source">Candler Hobbs/Georgia Tech</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>How does one get stuck studying frog tongues? Our study into the sticky, slimy world of frogs all began with a <a href="https://www.youtube.com/watch?v=LbNl3J8HXw4">humorous video</a> of a real African bullfrog lunging at fake insects in a mobile game. This frog was clearly an expert at gaming; the speed and accuracy of its tongue could rival the thumbs of texting teenagers.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/LbNl3J8HXw4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The frog that was the genesis of the authors’ tongue research.</span></figcaption>
</figure>
<p>Further YouTube research yielded amazing videos of frogs eating <a href="https://www.youtube.com/watch?v=6AILF4Spwpo">mice</a>, <a href="https://www.youtube.com/watch?v=b-K0KcbUWmI">tarantulas</a> and even other <a href="https://www.youtube.com/watch?v=2kwrWl8zWdg">frogs</a>. </p>
<p>The versatile frog tongue can grab wet, hairy and slippery surfaces with equal ease. It does a lot better than our engineered adhesives – not even household tapes can firmly stick to wet or dusty surfaces. What makes this tongue even more impressive is its speed: Over 4,000 species of frog and toad <a href="http://psycnet.apa.org/psycinfo/1990-97523-000">snag prey faster than a human can blink</a>. What makes the frog tongue so uniquely sticky? <a href="http://dx.doi.org/10.1098/rsif.2016.0764">Our group aimed to find out</a>.</p>
<h2>Baseline frog tongue knowledge</h2>
<p>Early modern scientific attention to frog tongues came in 1849, when biologist Augustus Waller published the <a href="http://dx.doi.org/10.1098/rstl.1849.0010">first documented frog tongue study</a> on nerves and papillae – the surface microstructures found on the tongue. Waller was fascinated with the soft, sticky nature of the frog tongue and what he called:</p>
<blockquote>
<p>“the peculiar advantages possessed by the tongue of the living frog…the extreme elasticity and transparency of this organ induced me to submit it to the microscope.”</p>
</blockquote>
<p>Fast-forward 165 years, when biomechanics researchers Kleinteich and Gorb were the first to <a href="http://dx.doi.org/10.1038/srep05225">measure tongue forces in the horned frog</a> <em>Ceratophrys cranwelli</em>. They found in 2014 that frog adhesion forces can reach up to 1.4 times the body weight. That means the sticky frog tongue is strong enough to lift nearly twice its own weight. They postulated that the <a href="http://dx.doi.org/10.1098/rsos.150333">tongue acts like sticky tape or a pressure-sensitive adhesive</a> – a permanently tacky surface that adheres to substrates under light pressure.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/155018/original/image-20170131-3244-7r5phb.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">Frog tongue holding up a petri dish just with its stickiness.</span>
<span class="attribution"><span class="source">Alexis Noel/Georgia Tech</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To begin our own study on sticky frog tongues, we filmed various frogs and toads eating insects using high-speed videography. We found that the frog’s tongue is able to capture an insect in under 0.07 seconds, five times faster than a human eye blink. In addition, insect acceleration toward the frog’s mouth during capture can reach 12 times the acceleration of gravity. For comparison, astronauts normally experience around three times the acceleration of gravity during a rocket launch.</p>
<h2>On to the materials testing</h2>
<p>Thoroughly intrigued, we wanted to understand how the sticky tongue holds onto prey so well at high accelerations. We first had to gather some frog tongues. Here at Georgia Tech, we tracked down an on-campus biology dissection class, who used <a href="https://en.wikipedia.org/wiki/Northern_leopard_frog">northern leopard frogs</a> on a regular basis.</p>
<p>The plan was this: Poke the tongue tissue to determine softness, and spin the frog saliva between two plates to determine viscosity. Softness and viscosity are common metrics for comparing solid and fluid materials, respectively. Softness describes tongue deformation when a stretching force is applied, and viscosity describes saliva’s resistance to movement. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1067&fit=crop&dpr=1 600w, https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1067&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1067&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1340&fit=crop&dpr=1 754w, https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1340&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/155021/original/image-20170131-3269-v89zmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1340&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When the indentation head pulls away from the tongue, it adheres and stretches.</span>
<span class="attribution"><span class="source">Alexis Noel/Georgia Tech</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Determining the softness of frog tongue tissue was no easy task. We had to create our own indentation tools since the tongue softness was beyond the capabilities of the traditional materials-testing equipment on campus. We decided to use an indentation machine, which pokes biological materials and measures forces. The force-displacement relationship can then describe softness based on the indentation head shape, such as a cylinder or sphere.</p>
<p>However, typical heads for indentation machines can cost US$500 or more. Not wanting to spend the money or wait on shipping, we decided to make our own spherical and flat-head indenters from stainless steel earrings. After our tests, we found frog tongues are about as soft as brain tissue and 10 times softer than the human tongue. Yes, we tested brain and human tongue tissue (post mortem) in the lab for comparison.</p>
<p>For testing saliva properties, we ran into a problem: The machine that would spin frog saliva required about one-fifth of a teaspoon of fluid to run the test. Sounds small, but not in the context of collecting frog spit. Amphibians are unique in that they <a href="http://dx.doi.org/10.1111/j.1463-6395.1969.tb00527.x">secrete saliva through glands located on their tongue</a>. So, one night we spent a few hours scraping 15 dead frog tongues to get a saliva sample large enough for the testing equipment.</p>
<p>How do you get saliva off a frog tongue? Easy. First, you pull the tongue out of the mouth. Second, you rub the tongue on a plastic sheet until a (tiny) saliva globule is formed. Globules form due to the long-chain mucus proteins that exist in the frog saliva, much like human saliva; these <a href="http://dx.doi.org/10.1007/BF00305337">proteins tangle like pasta when swirled</a>. Then you quickly grab the globule using tweezers and place it in an airtight container to reduce evaporation.</p>
<p>After testing, we were surprised to find that the saliva is a two-phase viscoelastic fluid. The two phases are dependent on how quickly the saliva is sheared, when resting between parallel plates. At low shear rates, the saliva is very thick and viscous; at high shear rates, the frog saliva becomes thin and liquidy. This is similar to paint, which is easily spread by a brush, yet remains firmly adhered on the wall. Its these two phases that give the saliva its reversibility in prey capture, for adhering and releasing an insect.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/26xFAMpG2R8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A South American horned frog demonstrates capturing a cricket in this slow motion video.</span></figcaption>
</figure>
<h2>To catch a cricket</h2>
<p>How does soft tissue and a two-phase saliva help the frog tongue stick to an insect? Let’s walk through a prey-capture scenario, which begins with a frog tongue zooming out of the mouth and slamming into an insect.</p>
<p>During this impact phase, the tongue deforms and wraps around the insect, increasing contact area. The saliva becomes liquidy, penetrating the insect cracks. As the frog pulls its tongue back into the mouth, the tissue stretches like a spring, reducing forces on the insect (similar to how a bungee cord reduces forces on your ankle). The saliva returns to its thick, viscous state, maintaining high grip on the insect. Once the insect is inside the mouth, the eyeballs push the insect down the throat, causing the saliva to once again become thin and liquidy. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fwThZXXXdTc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Frogs’ eyeballs actually help them swallow their food by physically pushing what’s in the mouth back into the throat.</span></figcaption>
</figure>
<p>It’s possible that <a href="http://dx.doi.org/10.1098/rsif.2016.0764">untangling the adhesion secrets of frog tongues</a> could have future applications for things like high-speed adhesive mechanisms for conveyor belts, or fast grabbing mechanisms in soft robotics.</p>
<p>Most importantly, this work provides valuable insight into the biology and function of amphibians – 40 percent of which are in <a href="http://www.iucnredlist.org">catastrophic decline or already extinct</a>. Working with conservation organization <a href="http://www.amphibianfoundation.org">The Amphibian Foundation</a>, we had access to live and preserved species of frog. The results of our research provide us with a greater understanding of this imperiled group. The knowledge gathered on unique functions of frog and toad species can inform conservation decisions for managing populations in dynamic and declining ecosystems.</p>
<p>While it’s not easy being green, a frog may find comfort in the fact that its tongue is one amazing adhesive.</p>
<hr>
<p><em>Mark Mandica of <a href="http://www.amphibianfoundation.org">The Amphibian Foundation</a> collaborated on the <a href="http://dx.doi.org/10.1098/rsif.2016.0764">research published in Journal of the Royal Society Interface</a> and coauthored this article.</em></p><img src="https://counter.theconversation.com/content/72064/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This material is based upon work supported by the National Science Foundation Graduate Research Fellowship (DGE-1148903).</span></em></p><p class="fine-print"><em><span>David Hu 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>How do a frog’s tongue and saliva work together to be sticky enough to lift 1.4 times the animal’s body weight? Painstaking lab work found their spit switches between two distinct phases to nab prey.Alexis Noel, PhD Student in Biomechanics, Georgia Institute of TechnologyDavid Hu, Associate Professor of Mechanical Engineering and Biology, Adjunct Associate Professor of Physics, Georgia Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/495682015-11-03T11:08:30Z2015-11-03T11:08:30ZEleven body fluids we couldn’t live without<figure><img src="https://images.theconversation.com/files/99266/original/image-20151022-15414-1nhuve6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Blood is just one of the body fluids we need to survive. </span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-193429070/stock-photo-blood-donor-at-donation-with-a-bouncy-ball-holding-in-hand.html?src=57IVDqZZgssJrc82KtPa8A-1-23">Blood bag via www.shutterstock.com.</a></span></figcaption></figure><p>How is a human being like a fish? </p>
<p>Just as a fish never stops to think about the water in which it spends its entire life, so do many human beings rarely pause to consider the body fluids that make our lives possible. </p>
<p>Though not always fit for polite conversation, even the less pleasant among them play a crucial role in maintaining health. By learning a bit more about 11 of these body fluids, we can develop a deeper appreciation for the beauty and complexity of our own biology. What exactly are these fluids, and what often unheralded contributions do they make?</p>
<h2>1. Bile</h2>
<p>Bile is a brown to dark green fluid that is produced by the liver, stored in the gallbladder (a synonym for bile is gall), and released into the intestines when we eat. It is partly responsible for the color of vomitus and stool. Its most important ingredient is bile salts, which function like soap to break down dietary fats, enabling them and fat-soluble vitamins such as A, D and E to be absorbed. They also help to prevent the cholesterol-containing bile in the gallbladder from forming gallstones.</p>
<p>Curiously, about 15 grams of bile salts are excreted into the intestine each day, yet the human body contains only about five grams in total. How is this possible? The answer is that bile salts are recycled, being reabsorbed into the blood through the small intestine and then secreted again by the liver. </p>
<p>Some intestinal diseases, such as Crohn’s disease, can damage the part of the small bowel where bile salts are reabsorbed, predisposing patients to gallstones.</p>
<h2>2. Blood</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/99263/original/image-20151022-15421-la6k9h.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">Give a little.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-193429070/stock-photo-blood-donor-at-donation-with-a-bouncy-ball-holding-in-hand.html?src=57IVDqZZgssJrc82KtPa8A-1-23">Blood donation via www.shutterstock.com.</a></span>
</figcaption>
</figure>
<p>Perhaps the most important body fluid of all is blood. The average adult contains about six liters of blood, which functions to transport oxygen to cells, carry metabolic waste products such as carbon dioxide away from cells and transport infection-fighting white blood cells, glucose, hormones and other essential substances throughout the body. Blood also contains cell fragments called platelets and clotting factors that help to seal leaks that may develop in blood vessels.</p>
<p>An adult’s body contains about 25 trillion red blood cells – about one-third of all the body’s cells. Red blood cells survive on average about 120 days, which means that every second of every day, an adult human produces about two million red blood cells. If lined up end to end, the tiny blood vessels in which gas is actually exchanged, the capillaries, would reach a length of about 60,000 miles, long enough to encircle the earth more than twice.</p>
<h2>3. Menstrual fluid</h2>
<p>The average woman menstruates every 28 days over 42 years of her life, for a total of about 520 menstrual periods. The average volume of menstrual fluid is approximately 40 milliliters, or about 2.5 tablespoons in total. The fluid itself is about one-half blood, and also contains tissue from the inner lining of the uterus, mucus and secretions from the vagina. If the amount of bleeding is abnormally high, it can result in anemia, a deficit of red blood cells.</p>
<p>Along with blood and semen, menstrual fluid is one of the body fluids with the strongest psychological and cultural overtones. Traditionally, the onset of menstruation is associated with the transition from childhood to adulthood, and the onset of each menstrual cycle has long provided the best evidence that a woman is not pregnant. Some societies and faith traditions have sequestered menstruating women, although menstrual fluid is no more biologically hazardous than blood.</p>
<h2>4. Mucus</h2>
<p>Mucus sounds unpleasant, but none of us would be here without it. A slippery, clear liquid produced by mucous glands, it lines the cells of the bronchi in the lungs, the stomach and intestines, the urinary and reproductive tracts, and the eyes and ears. Mucus contains a variety of important substances, including antiseptic enzymes, antibodies and mucins that give mucus its gel-like properties. The average adult produces about one liter of mucus per day.</p>
<p>Mucus keeps the lining of the respiratory system from drying out and also filters out dust and infectious agents in the air we breathe. Microscopic hair-like projections from the cells lining the lung’s air passages help to propel the mucus back up toward the mouth at a speed of about one millimeter per minute, where it can be swallowed or expectorated. </p>
<p>Patients with cystic fibrosis have a genetic mutation that makes their mucus too thick, undermining this important defense against infection.</p>
<h2>5. Pus</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=787&fit=crop&dpr=1 600w, https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=787&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=787&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=989&fit=crop&dpr=1 754w, https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=989&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/99253/original/image-20151021-15426-22wldr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=989&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Any pus? Watercolour by J. Cats, 1787, after B. Maton.</span>
<span class="attribution"><span class="source">Wellcome Library, London</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Pus sounds even more disagreeable but serves as a sign that the immune system is working. A white, yellow or brown viscous fluid that accumulates at sites of infection, pus usually consists of bacteria, white blood cells, and other proteins and cell debris. Pus under the skin is often found in a pimple, but deeper in the body a larger collection is known as an abscess. Pimples and abscesses represent the body’s attempt to contain the spread of an infection.</p>
<p>For many centuries, one of the dictums of the barber-surgeon was, “Where there is pus, evacuate it,” thereby purging the infection from the body. Until several decades ago, drainage required a surgical procedure. Today, however, many abscesses are drained using just a needle and catheter, with ultrasound or CT imaging for guidance. This less invasive approach reduces the need for anesthesia, recovery time and cost.</p>
<h2>6. Semen</h2>
<p>Semen, the fluid released by males at ejaculation, generally contains spermatozoa, the gametes that fertilize the female egg, though this is not the case for males who have undergone the most common sterilization procedure, vasectomy. </p>
<p>In addition to providing a medium through which sperm can “swim,” semen also contains fructose, a sugar that nourishes the sperm, as well as alkaline secretions that help to neutralize the normally acidic environment of the vagina.</p>
<p>Females are born with all the eggs they will ever have, but males continuously produce gametes from puberty onward, and the average healthy male’s ejaculate of about five milliliters contains approximately 300 million spermatozoa. </p>
<p>Why such large quantities are produced when only one sperm can fertilize an egg is a bit of a puzzle, but one explanation may be that the competition between sperm helps to select for the fittest.</p>
<h2>7. Saliva</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=943&fit=crop&dpr=1 754w, https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=943&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/99269/original/image-20151022-15426-1r7lqcw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=943&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Drool, baby, drool.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-3227780/stock-photo-cute-baby-drooling.html?src=G0E1zC4Cs22yU0iEkGYcTw-1-0">Baby via www.shutterstock.com</a></span>
</figcaption>
</figure>
<p>Saliva is secreted by salivary glands in and around the mouth. The average adult produces about a liter of saliva per day, with peak secretion at meals. Like mucus, saliva contains antibacterial enzymes and antibodies, as well as mucus itself. Saliva helps to moisten food, which is important to lubricate chewing and swallowing. It also enhances taste, because if the chemicals in food were not in a liquid medium, they could not be detected by taste receptors. </p>
<p>Some of the enzymes in saliva also begin to break down substances in food, such as starches, which are broken down by amylase. Because such enzymes are generally neutralized within seconds after reaching the highly acidic secretions in the stomach, they probably function mainly to break down food particles trapped between teeth, helping to prevent cavities. </p>
<p>Patients who lack sufficient saliva have much higher rates of tooth decay and gum disease.</p>
<h2>8. Sweat</h2>
<p>Sweat, like saliva, consists almost entirely of water, though it also contains minerals that account for its salty taste. Sweat production can vary widely between one-tenth of a liter and eight liters per day, and during intense exercise, an adult may produce two liters per hour or more. The body’s three million sweat glands come in two types. Eccrine glands are found all over the body, with the highest density in palms and souls. Apocrine glands are located most prominently in the armpits.</p>
<p>Sweat’s most important role is thermoregulation, helping to cool the body when it begins to overheat. By comparison, dogs, which lack sweat glands, must pant to dissipate heat through evaporation. The brain stimulates sweating through nerves, and the rate is increased in response not just to heat but also emotional states. In contrast to heat-based sweating, the emotional type is associated with perspiration in only the palms, soles and armpits.</p>
<h2>9. Tears</h2>
<figure class="align-right zoomable">
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<figcaption>
<span class="caption">Engraving of the lacrimal gland.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Gray896.png">Henry Vandyke Carter, via Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>Tears are produced by the lacrimal glands above and lateral to the eye, and are spread over the eye’s surface by blinking. They are drained into the nasal cavity, which explains why people often get a runny nose when they cry. Tears serve three functions: to lubricate the eye, to remove irritants such as smoke (and a sulfuric acid-producing chemical from cut onions) and in association with emotional states such as sorrow and joy.</p>
<p>Dry eye syndrome, the most common eye disease, affects as many as one-third of elderly people, though it can occur at any time in life. The most common cause is decreased tear production, which in most patients occurs for no known reason, though it is associated with a variety of diseases and medications. The most common treatment involves, naturally enough, the use of eye drops.</p>
<h2>10. Urine</h2>
<p>The average adult produces about 1.5 liters of urine per day. Produced by the kidneys and stored by the bladder, urine contains many substances that must be removed from the body to maintain a state of health. These include the breakdown products of protein metabolism, which would become toxic if they were allowed to accumulate in the blood. Urine also serves as the principal means for removing excess salt and water from the body. </p>
<p>A common diagnostic procedure in medicine is urinalysis. Finding glucose in urine could indicate that a patient is suffering from diabetes mellitus, a disease that got its name in part from the fact that the urine of diabetic patients tastes sweet. Likewise, finding bacteria suggests that the patient is suffering from a urinary tract infection. Interestingly, most of the amniotic fluid that cushions a fetus in utero is made up of urine produced by the fetus’ kidneys.</p>
<h2>11. Vomitus</h2>
<p>Vomitus differs from the other body fluids discussed here because it is not produced under everyday circumstances. Everyone vomits at some point in their life in response to one of several types of stimuli. The balance center of the inner ear can induce vomiting, as in motion sickness. Another cause is irritation of the gastrointestinal tract by infections and poisons.</p>
<p>In some cases, vomiting purges the body of toxins, but in other cases vomitus contains only food. In either case, the fluid is usually highly acidic, because of the acids normally secreted by the stomach. In individuals who vomit frequently, such as patients with bulimia, this acid can erode the surface of the teeth and cause dangerous changes in the pH balance of the blood. The presence of blood in vomitus is generally a sign of bleeding from the esophagus or stomach.</p>
<p>This list of bodily fluids only scratches the surface. For every fluid that is regularly visible to the eye, there is another that, at least in health, we see only rarely. These include amniotic fluid, cerebrospinal fluid and the fluids that lubricate the surface of the heart and lungs, the abdominal organs and the joints, among many others. To get to know these fluids better is to gain deep insights into the biology of the human body in both health and disease.</p><img src="https://counter.theconversation.com/content/49568/count.gif" alt="The Conversation" width="1" height="1" />
By learning a bit more about these body fluids, we can develop a deeper appreciation for the beauty and complexity of our own biology.Richard Gunderman, Chancellor's Professor of Medicine, Liberal Arts, and Philanthropy, Indiana UniversityLicensed as Creative Commons – attribution, no derivatives.