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Heatstroke: What is heatstroke?

Woman experiencing a heatstroke
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Heatstroke is a consequence of being too hot for too long, causing your core temperature to rise. There are many different causes, which can include exercising during hot weather. Some susceptible people can even get heatstroke in the home if the temperature is too high. Heatstroke is a medical emergency, and must be treated immediately.

If you're planning on spending time outside during hot weather, you might wonder what heatstroke is and how you can avoid it.

This guide will cover:

  • What causes a heatstroke?
  • How long does heatstroke last?
  • What are the symptoms of heatstroke?
  • What is the difference between heatstroke and heat exhaustion?
  • How to prevent heatstroke
  • Treatments for heatstroke

What causes a heatstroke?

Heatstroke is your body’s reaction to being too hot. If your core temperature (inside your body rather than on your skin) rises above 40॰C for a long time, it can cause damage to your brain and other organs.

At temperatures below 40॰C, you can usually control your body temperature by sweating, removing clothes or moving to a cooler area. When you go above 40॰C, your body can lose the ability to control your temperature, and the severe symptoms of heatstroke can set in.

Heatstroke is the endpoint of several heat stress illnesses. This means you will often have less severe heat-related conditions symptoms before getting heatstroke.

Some people are more likely to get a heatstroke than others and may need to take action at lower temperatures to avoid it. If you work or do heavy exercise outside, especially when the weather is warm, you can be at a higher risk of heatstroke.

Children under the age of four, adults over 65, and those with health concerns also have a greater chance of developing the condition.

If you live in a city, the summer temperature is likely hotter than in rural areas. This is due to what’s known as the ‘heat island’ effect, where the material that makes up buildings and roads absorbs heat during the day and emits it at night. This causes the temperature at night to stay raised.

In cities, the indoor temperatures during summer can rise high enough to cause heatstroke, especially if the building does not have air conditioning.

First signs of heatstroke

How long does heatstroke last?

Heatstroke is a medical emergency that will need treatment in the hospital. How long a person would have to stay in the hospital is related to how much damage the heat has caused their brain and other organs.

Some people will recover relatively quickly once they have cooled down. Others may need to stay in hospital for some time, perhaps even in an intensive care unit.

Once out of the hospital, they’ll be more sensitive to heat for at least a week and will need to avoid high temperatures or heavy exercise. For people who have had heatstroke, it’s often advisable to talk to a doctor before starting to exercise again.

What are the symptoms of heatstroke?

Spending too much time in the sun can have various effects that need treatment, from sunburn to heat-related illnesses. Heatstroke affects everyone differently, and not all people will have the same symptoms. Some of the most common signs of heatstroke are:

  • A temperature of over 40॰C
  • Severe headache
  • Dizziness
  • Not sweating despite being very hot
  • Hot, red or dry skin
  • Muscle weakness or cramping
  • Nausea and vomiting
  • A rapid heartbeat
  • Fast breathing
  • Confusion
  • Seizures
  • Unconsciousness

If someone you’re with is showing some of these signs, they must get to a hospital quickly. Phone 999 and follow the advice you are given while waiting for an ambulance to arrive.

What is the difference between heatstroke and heat exhaustion?

Both heat exhaustion and heatstroke are conditions caused by the body getting too hot.

While the symptoms of heat exhaustion are not usually as severe, if left untreated, it can become heatstroke. Taking action early when you recognise the signs of heat exhaustion can prevent it from turning into heatstroke.

Heat exhaustion Heatstroke
  • Core body temperature over 38॰C
  • Headache
  • Confusion
  • Dizziness
  • Cramping
  • Fast heartbeat or breathing
  • Sweaty
  • Nausea and sickness
  • Core body temperature above 40॰C
  • Severe headache
  • Confusion
  • Dizziness
  • Cramping
  • Fast heartbeat or breathing
  • No sweating
  • Nausea and sickness
  • Seizures
  • Unconsciousness


You can test your core body temperature using a thermometer. Choose a digital or touch-free thermometer to accurately measure your body temperature quickly.

How to prevent heatstroke

Heat-related illnesses are strongly related to temperature. If the forecast shows a hot day approaching, you might need to think about taking extra suncare or changing your plans.

Some people have a higher risk of getting heatstroke because of age or other medical conditions. If you or a loved one is more likely to be affected from heat exhaustion or heatstroke, you should be even more careful in hot weather.

Things you can do to reduce your risk of heatstroke include:

  • Avoid exercising in high temperatures
  • Consider rescheduling outdoor activities to avoid the hottest time of day
  • Wear lightweight clothing and a hat to keep the sun off your head
  • Keep windows open, and curtains closed during the day to maintain a cooler temperature at home

Making sure you stay hydrated is one of the most important ways to avoid heatstroke and other heat-related illnesses. Actions you can take to prevent getting dehydrated include:

  • Have a drink of water first thing in the morning, and make sure you keep drinking throughout the day
  • Drink plenty of fluids when exercising – hydration products mixed with water can help make sure you stay hydrated
  • Always carry a bottle of water when you go out
  • Choose foods with high water content, like strawberries, watermelon and cucumber

Treatments for heatstroke

Heatstroke is a severe medical condition. If you suspect someone has heatstroke, call 999 for help straight away. There are several things you can do while waiting for medical assistance:

  • Move to a cooler environment, either indoors or in the shade
  • Try to cool down with fans, ice or a cold shower
  • If the person is conscious, encourage them to drink plenty of water
  • If the person is unconscious, put them in the recovery position

For more information about heat-related illnesses, visit our Online Doctor.

Heatstroke is a severe medical condition caused by the body getting too hot. By looking after yourself and others in hot weather, the likelihood of heatstroke can be significantly reduced.

If you’re spending time in the sunshine, always wear sun cream, cover your head and remember to look after yourself when you return inside. Read our advice on choosing the best sun cream for you and make sure you’re ready for warmer weather.

To help make your time in the sun as safe as possible, check out our travel advice for lots of other articles about self-care in the sunshine.

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