Keep fit, stay cool: how to prevent heat exhaustion

Published in Medicinewise Living

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Exercising when it’s hot can rapidly exhaust and overheat your body. Recognising the warning signs and acting fast could save your life.

How can my body overheat?

Your body can overheat if you exercise strenuously in very hot or humid weather. Dehydration, sunburn, and drinking alcohol can all reduce your body’s ability to sweat and cool.

Heat exhaustion can affect anyone, but very young children and older people are at greater risk. You are also at high risk if you:

  • are overweight
  • have diabetes
  • have kidney, heart or circulation problems
  • are not used to hot or humid weather.

Some medicines can affect sweating or body temperature. These include diuretics (which increase fluid loss) and some medicines for the treatment of high blood pressure and heart disease.

Certain medicines can also increase sensitivity to sunburn, including some antibiotics, medicines that suppress the immune system, treat cancer and mental health conditions.

What are the symptoms of heat exhaustion?

Heat exhaustion can make you feel extremely hot, tired and thirsty. You may also sweat heavily and urinate less than normal.

You may experience painful muscle cramps in your legs, arms, or abdomen. Other signs of heat exhaustion include:

  • pale or clammy skin
  • headache
  • dizziness or fainting
  • nausea or vomiting
  • rapid heartbeat (not from exercise).

What can be done to treat heat exhaustion?

Heat exhaustion can be managed using first aid. Heat stroke is a medical emergency and requires urgent professional medical attention (see What are the complications of heat exhaustion? below).

Stop, rehydrate and cool down

As soon as you notice any signs of heat exhaustion:

  • move to a cool or shaded area and lie down
  • apply cool water to skin or clothing
  • loosen or remove clothing
  • drink cool water or rehydration fluids; avoid caffeine or alcohol.

Also follow these steps if you are helping someone else who has heat exhaustion, but only give them cool fluids to drink if they are fully conscious and able to swallow.

How can I avoid heat exhaustion?

Stay hydrated

Drink water or non-alcoholic, non-caffeinated drinks before,during and after exercise — even if you're not thirsty.

Exercise in cooler weather

Avoid physical activity on very hot or humid days, and between 11am–3pm. If this is not possible, take regular breaks in the shade and rehydrate.

Avoid sunburn

Apply sunscreen with a high sun protection factor (SPF) that blocks both UVA and UVB rays. Use other sun protection measures including a brimmed hat and protective clothing.

Wear light clothing

Loose, lightweight clothing allows sweat to evaporate and cool you.

Slowly adjust to the heat

If you’re travelling abroad or to a hotter part of the country, it can take time to get used to heat or humidity, so arrive well before you do any strenuous physical activity. Try to build up the intensity of your exercise slowly.

What are the complications of heat exhaustion?

If heat exhaustion is not treated quickly, heat stroke may develop. Heat stroke happens when your body temperature rises to above 40°C and, if untreated, can permanently damage the brain, heart, and other organs.

The symptoms of heat stroke can be similar to heat exhaustion, but you may also stop sweating completely, become delirious or unsteady on your feet, have a fit or collapse.

When should I see a health professional?

Call an ambulance if you think you or someone else has heat stroke. Seek urgent medical attention if:

  • heat exhaustion symptoms don’t improve within 30 minutes of applying first aid
  • someone is at high risk of developing heat stroke, such as babies and older people.

Ask your doctor for advice before exercising in hot or humid weather, especially if you have a medical condition that restricts your fluid intake. Ask your health professional if any of your medicines can increase your risk of sunburn, dehydration, or heat exhaustion.

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