What happens to our bodies during intense heat
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What happens to our bodies during intense heat

What happens to our bodies during intense heat

September 6, 2021

2021’s summer hasn’t been the non-stop sunshine and blue skies many of us hoped for, but at the very least, we’re due some balmy September days this week.

With more sunshine than usual at this time of year, we’ve taken a look at what happens to your body in the heat, and what you can do to deal with it(1).

City living vs. suburban & rural

If you’re piling on to a busy bus or train during the sweltering heat, it can often feel that living in a city is more of a struggle than other, less crowded areas.

Well, there is some truth to places like London or other big cities feeling hotter than they would in other more tropical locations. Data shows that cities and urban areas are often hotter than more remote areas due to a number of factors such as wind chill, heat absorption, heat dispersion and city or building design(2).


So what happens to our body as we get hotter? The body is usually amazing at regulating our core temperature and it does this in a number of ways. As we heat up and our skin feels warmer the capillaries (small blood vessels) in our skin relax or “Vasodilate” to allow for more blood to be closer to the surface of the skin and therefore to lose heat through convection and thus lowering your core temperature(3). In doing this, blood pressure drops.

To meet the demand of this fall in blood pressure, the heart rate will increase. This compensation leads to sweating and if this happens for long periods of time throughout the day, such as in a heat wave, symptoms of lethargy, impaired concentration, muscle cramps and even fainting may occur.


Changes in the body which allow cooling also have an effect on a biochemical level. This will cause some of the signs and symptoms often associated with heat stroke such as fatigue, muscle cramps and lethargy. Further sweating leads to losing more water and salts through the pores in the skin and this can change the salt and acid base balance of the blood. If not replaced with adequate fluid intake it can cause our cells in the body to not function as we like. In severe cases this can lead to renal damage or increasing our risk of developing abnormal cardiac function or blood clots. Most of the time our body is able to regulate this by reabsorption of water or electrolytes by the kidney but in some people these regulatory mechanisms are not as robust(4). People who should be particularly careful are the elderly, those with pre-existing medical problems or on medications like diuretics or blood pressure medications. It is estimated that heat related complications lead to 2000 deaths a year in the UK(5, 6).


Simple tips if done in combination can add up to big results and make you feel much better during the heat.

Some of our top tips for staying cool and healthy this summer are:

  • Setting alarms to remind yourself to move from your desk and drink water.

  • Buying a reusable container is not only good for your carbon footprint but acts as an aide memoire to rehydrate

  • Reducing caffeine content and especially alcohol content which are both diuretics.

  • Taking a break from computer screens and closing curtains to stay in the shade.

  • Loose fitting light-coloured clothing is not only a fashion must but helps to keep you airy and cool as well as not absorbing the sun's rays.

  • Eating early in the morning, light meals more often and avoiding eating big meals which may make you feel tired due to the postprandial effects on blood glucose. Coupled with the heat can be a double whammy!

  • If you are struggling to sleep things like cool packs or wet cloths in areas closer to the core like your armpits, back of the neck or groin lower your core temperature quicker.

  • Foods like watermelon which are high in water content can be a nice way to gain extra hydration when bored of water!

  • If you’re mad enough to exercise in the heat, do so early in the morning or late at night, plenty of suncream and hydration before, during and after and don’t push yourself too hard!






5.https://www.theccc.org.uk/wp-content/uploads/2019/07/Outcomes-Heat-preventable-deaths-case-study.pdf 6. https://www.theguardian.com/environment/2021/may/30/heatwave-deaths-set-to-soar-as-uk-summers-become-hotter

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