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Curious Kids: if our bodies are happy at 37°C, why do we feel so unhappy when it’s too hot outside?

How come the inside of your body is happy at 37 degrees but when the outside temperature is 37 degrees your body is very unhappy? — Patrick, aged 8.

Great question, Patrick!

You’re right. Most people’s bodies are happiest when their inside temperature sits around a nice 36.5-37.5°C. These temperatures allow your body to work the best.

But your body temperature does go through small changes. It can be a bit lower when you’re asleep. It can also change during the day when you feel hungry, tired or cold. And when you’re sick, your temperature can rise. That’s when you might have a fever.

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A happy body

It’s really important to keep your body temperature at around 37°C otherwise you can overheat and get quite sick.

To do this, muscles, such as the ones in your arms and legs, tighten (or contract). This process generates, or “makes”, heat. Your blood then carries this heat around your body.

But to stop your inside temperature getting too high, for example when you’re exercising on a hot day, your body needs to lose some of that heat.

A young girl running in the park.
Running generates a lot of heat, which our body needs to get rid of to the air around us. Shutterstock

Warm blood travels through blood vessels close to your skin. This heat is then “lost” to the air around you.

If that’s not enough to cool you down, your body will also start sweating. This speeds up how you lose heat through your skin.

You usually feel the most comfortable when it’s around 18-24°C. This seems to be a nice temperature that allows any extra heat to escape into the air. But it’s also not so cold that you need to move around to keep warm.

Phew, it’s stinking hot!

Things that get in the way of losing heat through the skin can make you feel hot, such as wearing a woolly jumper in summer.

But you can also feel uncomfortable on a hot and humid day. That’s because the warm outside temperature makes it hard for you to lose heat from your skin to the air around you (because the air is already quite warm). And without a breeze, it’s even harder for the heat to be carried away.

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How to keep cool

If it’s very hot or humid, your body may find it hard to lose extra heat. So to keep cool on these days:

  • drink water often. This not only keeps your body happy, it gives you extra liquid to turn into sweat. Sweating helps you lose heat

  • avoid direct sunlight, and try to keep to the shade or places with a cool breeze

  • wear thin clothing and natural fibres, which can allow a clear flow of air

  • wear light-coloured clothing, as this can keep you cooler than darker colours

  • avoid running, jumping or riding your bike in the middle of the day

  • on hot days, jump in a pool, or try to escape the heat by putting on the air-conditioning inside

  • sit in front of a fan. This breeze carries heat away from your skin and into the air around you, cooling you down quickly.

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