Heat exhaustion and heatstroke are two potentially serious conditions that can occur if you get too hot.

They usually happen during a heatwave or in a hot climate, but can also occur when you're doing very strenuous physical exercise.

• Heat exhaustion is where you become very hot and start to lose water or salt from your body, which leads to the symptoms listed below and generally feeling unwell.
• Heatstroke is where the body is no longer able to cool itself and a person's body temperature becomes dangerously high (sunstroke is when this is caused by prolonged exposure to direct sunlight).

Heatstroke is less common, but more serious. It can put a strain on the brain, heart, lungs, liver and kidneys, and can be life-threatening.

If heat exhaustion isn't spotted and treated early on, there's a risk it could lead to heatstroke.

Signs and symptoms

Heat exhaustion or heatstroke can develop quickly over a few minutes, or gradually over several hours or days. 

Signs of heat exhaustion can include:

• tiredness and weakness
• feeling faint or dizzy
• a decrease in blood pressure
• a headache
• muscle cramps
• feeling and being sick
• heavy sweating
• intense thirst
• a fast pulse
• urinating less often and having much darker urine than usual 

If left untreated, more severe symptoms of heatstroke can develop, including confusion, disorientation, seizures (fits) and a loss of consciousness.

What to do

If you notice that someone has signs of heat exhaustion, you should:

• get them to lie down in a cool place – such as a room with air conditioning or somewhere in the shade
• remove any unnecessary clothing to expose as much of their skin as possible
• cool their skin – use whatever you have available, such as a cool, wet sponge or flannel, cold packs around the neck and armpits, or wrap them in a cool, wet sheet
• fan their skin while it's moist – this will help the water to evaporate, which will help their skin cool down
• get them to drink fluids – this should ideally be water, fruit juice or a rehydration drink, such as a sports drink

Stay with the person until they're feeling better. Most people should start to recover within 30 minutes.

If the person is unconscious, you should follow the steps above and place the person in the recovery position until help arrives (see below). If they have a seizure, move nearby objects out of the way to prevent injury.

When to get medical help

Severe heat exhaustion or heatstroke requires hospital treatment.

You should call 999 for an ambulance if:

• the person doesn't respond to the above treatment within 30 minutes
• the person has severe symptoms, such as a loss of consciousness, confusion or seizures

Continue with the treatment outlined above until the ambulance arrives. 

If the person is feeling better after using the above measures, but you have any concerns about them, contact your GP or NHS 111 for advice.

Who's most at risk?

Anyone can develop heat exhaustion or heatstroke during a heatwave or while doing heavy exercise in hot weather. However, some people are at a higher risk.

These include:

• elderly people
• babies and young children
• people with a long-term health condition, such as diabetes or a heart or lung condition
• people who are already ill and dehydrated (for example, from gastroenteritis)
• people doing strenuous exercise for long periods, such as military soldiers, athletes, hikers and manual workers

You're more likely to experience problems if you're dehydrated, there's little breeze or ventilation, or you're wearing tight, restrictive clothing.

Certain medications can also increase your risk of developing heat exhaustion or heatstroke, including diuretics, antihistamines, beta-blockers, antipsychotics and recreational drugs, such as amphetamines and ecstasy.

How to prevent heat exhaustion and heatstroke

Heat exhaustion and heatstroke can often be prevented by taking sensible precautions when it's very hot.

During the summer, check for heatwave warnings, so you're aware when there's a potential danger. The government uses a system called Heat-Health Watch to warn people about the chances of a heatwave. This is a system of four different warning levels based on the expected temperature.

Public Health England (PHE) has also published a Heatwave plan for England (PDF, 1.19Mb), which suggests following the advice below during a heatwave to help prevent heat-related illnesses.

Stay out of the heat

• Keep out of the sun between 11am and 3pm.
• If you have to go out in the heat, walk in the shade, apply sunscreen and wear a hat and light scarf.
• Avoid extreme physical exertion.
• Wear light, loose-fitting cotton clothes.

If you're travelling to a hot country, be particularly careful for at least the first few days, until you get used to the temperature.

Cool yourself down

• Have plenty of cold drinks, and avoid excess alcohol, caffeine and hot drinks.
• Eat cold foods, particularly salads and fruit with a high water content.
• Take a cool shower or bath.
• Sprinkle water over your skin or clothing, or keep a damp cloth on the back of your neck.

If you’re not urinating frequently or your urine is dark, it's a sign that you're becoming dehydrated and need to drink more.

Keep your environment cool

• Keep windows and curtains that are exposed to the sun closed during the day, but open windows at night when the temperature has dropped.
• If possible, move into a cooler room, especially for sleeping.
• Electric fans may provide some relief.
• Turn off non-essential lights and electrical equipment, as they generate heat.
• Keep indoor plants and bowls of water in the house, as these can cool the air.

In the longer term, it can help to have your loft and cavity walls insulated, as this will keep the heat in when it's cold and keep it out when it's hot. Using light-coloured, reflective external paint on your house may also be useful.

Look out for others

• Keep an eye on isolated, elderly, ill or very young people and make sure they are able to keep cool.
• Ensure that babies, children or elderly people are not left alone in stationary cars.
• Check on elderly or sick neighbours, family or friends every day during a heatwave.
• Be alert and call a doctor or social services if someone is unwell or further help is needed.

Read about how to prepare for a heatwave.