Nearly two weeks into the longest heatwave in seven years, the UK has been basking in temperatures of up to 32C. But while the weather is welcome for many, not everyone is so lucky - researchers estimated that up to 760 people have died due to the heat.
The elderly and the very young can be particularly vulnerable and heat illnesses - including heat stroke - can happen even if someone is well hydrated if the heat is more than the body can handle.
Heat stroke occurs when the body’s ability to dissipate heat is overwhelmed and it can’t keep itself cool. This can be because of strenuous exercise and/or the temperature of the environment.
To counter a rise in temperature, the body increases sweat production and dilates the small blood vessels in the skin to bring heat to the surface. But higher humidity and temperatures mitigate this effect and continued exposure to heat can lead to a heat illness. Heat cramps are the first step in this process, followed by heat exhaustion and eventually heat stroke.
Severe, moderate, mild
Heat stroke is severe and can lead to brain damage and death if not treated. It significantly increases body temperature and affects our mental state.
People with heat stroke become confused, irritable, hallucinate and can even go into a coma. They may have difficulty walking, muscle tremors, a pulse greater than 130 beats per minute, and breathe faster than normal. The body’s temperature can rise to greater than 40C.
This constellation of symptoms can look like someone has taken a toxic ingestion of cocaine or is having a reaction to a drug like aspirin, a serious infection or alcohol withdrawal.
Someone with heat stroke must have their body temperature lowered immediately.
To do this patients have to be completely naked while warm water is sprayed over the body and a fan directed towards them. Warm water is used to prevent shivering, which is a mechanism the body uses to generate heat.
Cooling is stopped once their temperature reaches 39C to prevent overshooting to a hypothermic state - when the body’s core temperature gets too low. Almost everyone with heatstroke is admitted to the hospital to monitor electrolytes in the blood and hydration, as well as to evaluate other problems such as organ dysfunction.
Other heat illnesses aren’t as severe. Mild heat illness cause heat cramps for example. These are painful contractions of the large muscles groups that come from strenuous exercise in the heat. Heat cramps don’t affect our mental capacities or lift our temperature too much.
Drinking alcohol, fatigue, and being ill before exercising increase your chance of getting cramps and other heat illnesses. Treatment involves rest, moving to a cool environment and ensuring adequate hydration and electrolyte replacement by oral drinks or intravenous hydration.
Heat exhaustion is a moderate heat illness involving total body water depletion and minor hyperthermia. People may have nausea, vomiting, lightheadedness, signs of dehydration, and fatigue.
The body temperature rises, but is still usually less than 40C. Heat exhaustion also doesn’t affect brain function. Treatment is the same as for heat cramps and the prognosis is excellent as major organ systems are only minimally affected. People with heat exhaustion may need to be looked at by a doctor but are usually able to go home.
The body’s cooling system
Our body works best with an internal temperature of 37C. To maintain a constant temperature the body uses homestatic mechanisms, such as shivering and sweating, to generate or dissipate heat. To cool down, our bodies use conduction, convection, evaporation, and radiation.
Conduction involves direct physical contact with cooler objects - an example might be touching your hands to a glass of ice water. But this only accounts for 2% of the heat we lose.
Convection, which accounts for around 10% of heat loss, involves the heat transferring to air or water around the body, for example by using a fan to move cool air around the body or a cold shower.
About 35% of our heat loss comes from evaporation. While we sweat, other animals have other evaporation mechanisms; dogs pant and kangaroos lick their forearms.
By far the biggest way of losing heat is through radiation, which transfers heat away from our bodies in the form of electromagnetic waves and can account for about 65% of heat loss. Unfortunately once ambient temperatures are greater than 35C, radiation becomes ineffective.
And all of these different heat regulators can be influenced by other factors including humidity, clothing, hydration and acclimatisation.
Preventing a heat illness
There is some research into the genetic factors that predispose certain people to heat illness. Some drugs appear to help prevent heat illness in animal tests. But the key to combating a rising temperature and a heat illness is prevention.
Minimise strenuous activity in hot weather, change your environment by staying in air conditioned buildings, use fans, stay hydrated and limit your alcohol and drug consumption.
Infants, the elderly, and those with pre-existing illnesses can’t modulate heat exposure as well as others and must take special precautions. Athletes also need to be aware. Some people acclimatise to hot environments over time but they are still susceptible to heat illnesses.
So, on hot days, grab a bottle of ice water, head to a favorite cool, inside environment and opt for a relaxing activity if you want to prevent becoming a victim of the heat.