18th July, 202210 min read

Heat exhaustion vs heat stroke: signs and treatments

Medically reviewed

All of Healthily's articles undergo medical safety checks to verify that the information is medically safe. View more details in our safety page, or read our editorial policy.

We all enjoy getting outside on a sunny day – but with good weather you also run the risk of getting heat exhaustion or heatstroke. These conditions might catch you by surprise. Maybe you signed up for a charity run, race day has arrived and it’s blazing hot. Or perhaps you’re on holiday, you fell asleep on the sun lounger and you’ve woken up feeling dizzy. Either way, heat-related illness can affect anyone. And yes, it can make you feel a bit embarrassed when it sneaks up on you.

But don’t let that put you off getting help – while heat exhaustion is usually mild, heatstroke is serious and requires urgent medical help.

Who is at risk of heat exhaustion and heatstroke?

Anyone can get heat exhaustion or heatstroke, but those particularly at risk include:

  • anyone doing hard exercise or sports such as long-distance running in hot weather
  • babies and toddlers under the age of 4 and people aged over 65
  • being obese
  • sudden exposure to high temperatures – such as a heat wave or travelling to a hot part of the world
  • people taking certain medications such as diuretics (‘water tablets’), and antipsychotics used to treat some mental health conditions, as you’re more likely to get dehydrated
  • using recreational drugs such as ecstacy, amphetamines or cocaine
  • having a chronic health condition such as diabetes, or heart, lung or kidney disease

So how can you prevent heat exhaustion and heatstroke? How can you spot the signs? And how can you tell the difference so you know what kind of treatment you need? Read on, we’ve got you…

Top tips to prevent heat exhaustion and heatstroke

How to survive in a heatwave

  • protect yourself against sunburn: Use sunscreen of SPF 30 or higher and wear loose clothing made from natural fibres (think cotton and linen) to stay cool, especially if you’re sightseeing in hot weather. Wear a broad brimmed hat and sunglasses
  • stay hydrated: Drink plenty of fluids to help replace the salt and fluid you lose through sweating. It’s especially important if you’re exercising on a warm day
  • take regular water breaks, whatever you’re doing: Don’t wait until you’re thirsty before drinking. Feeling thirsty can sometimes be a later symptom of dehydration, when you’ve already lost a lot of body water
  • try to avoid alcohol: It can cause dehydration and being tipsy can also reduce your awareness of early symptoms of heat exhaustion
  • skip your lunchtime run: Avoid exercise in hot weather when the sun is strongest (between 11am and 3pm). Try to exercise during cooler parts of the day
  • keep cool: Take cool showers or baths. If you start to feel hot put a damp cool, damp flannel on the back of your neck to help cool you down
  • keep your home cool: Close blinds or curtains during the day. If it’s hotter outside than in your house, keep your windows closed but open them at night, if you can, when the temperature drops
  • adjust your body: If you’re not used to hot weather and you travel to a hot part of the world or experience a heat wave, limit your time in the heat until you’ve adjusted to hotter weather
  • be medication aware: If you take medication that might increase your risk of a heat-related illness, avoid the heat, be aware of the symptoms of overheating and act quickly if they happen
  • don’t fall asleep in your car on a hot day: Even if the windows are open it can become very hot quickly and increase the risk of your body temperature rising. Keep babies and small children cool on car journeys on a hot day – shade them from the sun, open windows, make sure they are not overdressed and keep them well hydrated with cold drinks. If you’re on a long car journey take regular breaks to cool them down

Heat exhaustion vs heatstroke: what’s the difference?

Both heat exhaustion and heatstroke are caused by your body being exposed to too much heat. It’s possible to get them inside or outside – even if it’s not sunny.

Heat exhaustion

This happens when your body overheats. It tries to cool down by sweating, your pee gets more concentrated (to preserve water) and you feel thirsty. If your body can’t get rid of the extra heat, your body temperature rises to between 38–40°C.

Causes of heat exhaustion

  • hot weather
  • exercising in the heat – known as exertional heat illness
  • dehydration
  • drinking alcohol in hot weather
  • overdressing in the heat, especially in clothes that don’t allow your sweat to evaporate easily such as polyester and synthetic fibres

Heat exhaustion is usually a milder illness than heatstroke, where your body temperature rises even higher and causes serious problems. But if heat exhaustion isn’t treated properly, it can lead to heatstroke.

Classic heatstroke

Unlike heat exhaustion, heatstroke is a medical emergency that needs immediate treatment. It happens when your body temperature becomes dangerously high – above 40°C. This can damage your organs such as your lungs, kidneys and liver and, if left untreated, it can be fatal. It can happen during heat waves or long spells of very hot weather.

What is sunstroke?

Sunstroke is a form of heatstroke. The symptoms and risks are the same but it only happens because of being exposed to too much direct sunlight – such as falling asleep in the sun. Sunstroke can also be linked with other problems such as severe sunburn.

What are the symptoms of heat exhaustion and heatstroke?

Heat exhaustion symptoms

Symptoms may come on suddenly, especially if you’re moving around in hot weather. Symptoms include:

  • cool, moist, pale skin
  • heavy sweating
  • feeling faint or dizzy
  • tiredness and fatigue
  • muscle cramps in your arms and legs
  • nausea
  • headache
  • feeling anxious
  • feeling very thirsty
  • tummy cramps
  • temperature of 38°C or higher
  • fast breathing

Symptoms are the same in adults and children, although children can also become sleepy and floppy.

Heatstroke symptoms

Symptoms are triggered when your body temperature hits 40°C or above and it can no longer cool itself. Symptoms include:

  • confusion, agitation, slurred speech and irritability
  • no sweating despite being very hot
  • severe, throbbing headache
  • hot, flushed or red skin
  • fast, shallow breathing
  • nausea and vomiting
  • very fast heart rate
  • severe muscle pain
  • yellowing of your eyes or skin
  • dizziness or feeling faint
  • feeling anxious
  • seizures and blacking out
  • collapse

What can you do to treat heat exhaustion and heatstroke?

Treating heat exhaustion

If someone has symptoms of heat exhaustion, follow these steps and they should cool down within 30 minutes:

  • move to a cool place such as the shade or an air-conditioned room
  • lie down and raise their feet slightly
  • drink plenty – ideally water but sports drinks are OK
  • spray or sponge yourself or them with cool water
  • fan them

Always stay with someone who has heat exhaustion until they’re feeling better. If they’re still feeling unwell after 30 minutes, it could be heatstroke so get urgent medical help.

Treating heatstroke

Heatstroke is a medical emergency. If you thinks someone is suffering from heatstroke, follow these steps:

  • call an ambulance immediately and stay with the person until it arrives
  • while you’re waiting, move them to a cool place, take any excess clothing off them, fan them and wet their skin with cool wet towels. If you have any ice packs, place them on the person’s armpits, neck and back

Once in hospital, doctors will try to reduce the person’s body temperature as safely and quickly as possible by using cold baths or ice packs. Doctors may also give them oxygen to help with breathing and intravenous fluids (directly into a vein) to get fluid, salt and sugar into the person’s body.

How can your pharmacist help with heat exhaustion?

You can reduce your risk for heat exhaustion with a trip to your pharmacy. Go for rehydration sachets and ice packs if it’s likely you may be in the heat for a long time, and stock up on sunscreen to reduce your risk of sunburn.

How long does it take to recover from heat exhaustion and heatstroke?

Most people recover from heat exhaustion within 30 minutes so you should get medical advice if you don’t feel better after this. Heatstroke takes longer as it can continue to cause inflammation in your body for some time following treatment. This means that if you’ve needed treatment for heatstroke, don’t exercise or do any strenuous movement – including walking for long periods – for a week. When you do exercise again, only do so when it’s cool, and start light and slowly – build up over two weeks. You’re more likely to make a good recovery from heatstroke if you’re in good health and your treatment was quick.

Are there any long term effects of heatstroke?

If you’ve had heatstroke in the past it means you’re more at risk of suffering from it again, so make sure you take care on hot days in the future.

Fortunately, most younger people recover well from heatstroke but in older people – over the age of 60 – with severe heatstroke, almost half may die as a result.

Some people with existing chronic health conditions who recover may have longer-term problems because of damage to their organs, such as to their kidneys, lungs or liver.

Your health questions answered

‘Do I have heat exhaustion or COVID?’

“Some symptoms of COVID-19 can be very similar to those of heat exhaustion, such as feeling unwell, having a temperature, fatigue and being short of breath so it can be very difficult to tell them apart,’ says Healthily expert, Dr Roger Henderson. “If you have symptoms and think you’re at risk of heat exhaustion, it’s best to speak to a doctor and do a lateral flow test for COVID-19. If the lateral flow test is negative, your doctor will help you work out what’s going on. If you think it’s heat exhaustion, follow the self-care tips above, like making sure you’re drinking enough fluids.”

‘How can I tell if my child has heatstroke?’

“Heatstroke in your child is a possibility if they have been exposed to high temperatures, they have a temperature higher than 40°C and are very unwell with symptoms such as confusion, hallucinations and floppiness. Other symptoms can include rapid breathing, a fast heart rate, vomiting, diarrhoea and flushed, warm skin,” says Dr Henderson.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.