The right way to handle heat exhaustion

Emily Osborne Emily Osborne Regional Health and Safety Trainer at Nuffield Health
Heat exhaustion is a potentially serious condition that usually occurs when we’re unprepared and dehydrated. Prevention is always the best course of action and knowing how to prepare and spot the signs can help keep you safe and make your time in the summer sun a lot more enjoyable.

In this article, we take a look at heat-related illnesses, the symptoms you need to watch out for, and when to seek medical assistance for heat stroke.

What is heat exhaustion?

Heat exhaustion occurs when we overheat and spend too much time in the sun. It typically occurs when our temperature rises above 38°C and is our body’s natural response to losing too much water and salt when we sweat.

Heat exhaustion and the symptoms associated with it can vary from mild to severe. If you’ve spent the day in the sun and haven’t drunk enough water, you’ll probably feel more tired than usual, a little nauseous or dizzy, and in need of a big drink.

Serious cases of heat exhaustion can result in heat stroke, which is a similar, more severe condition that requires immediate medical attention.

Heat stroke

Heat stroke is a very serious condition that’s caused by prolonged dehydration and sun exposure.

It occurs when the body's temperature regulation system fails, causing the body’s core temperature to soar to 40°C or higher.

Some early signs of heat stroke to look out for include:

  • High body temperature (104°F or higher)
  • Confusion
  • A rapid pulse
  • Agitation
  • Slurred speech
  • Hot, dry skin (sweating may be absent)
  • A throbbing headache
  • Nausea or vomiting
  • Flushed skin
  • Shallow breathing

Whilst heat exhaustion can be managed and minimised by getting into the shade and rehydrating, this is not the case if any of these symptoms are present.

If you suspect you or someone you know is suffering from heat stroke, it’s vital you seek immediate medical intervention, as heat stroke can be fatal if left untreated.

What causes it?

Heat exhaustion is caused when our body loses too much water and salt as we sweat. Because we sweat more in the summer, most people experience heat exhaustion when they’ve been out having fun in the sun all day.

If you’re not used to the heat or the climate that you’re in, we recommend acclimatising before you spend time in the sun. Heat exhaustion is typically avoidable, if you prepare, stay hydrated throughout the day, and don’t spend long periods in direct sunlight.

Exercising in hot or humid weather can also accelerate the rate at which we perspire, leading to dehydration and heat exhaustion.

The climate conundrum

The reality of climate change is that hot summers and intense heatwaves are now commonplace in the UK.

As temperatures continue to rise, the strain our erratic weather puts on hospitals also increases, with increased admissions to A&E during heatwaves becoming more and more common.

People living in urban and economically disadvantaged areas are at higher risk of complications during a heatwave because of the urban heat island effect, where built-up areas get significantly warmer than their rural surroundings.

Whilst a hot summer can be seen as a welcome break from the dreary winters we’re used to in the UK, it’s important we recognise that these temperatures are not ‘normal’, and that we all need to be extra vigilant when spending time in the sun during these abnormally intense heatwaves.

What are the symptoms?

Symptoms of heat exhaustion are less severe than with heat stroke, but should never be ignored.

They include:

  • Heavy sweating
  • Pale skin
  • Weakness and fatigue
  • Dizziness and nausea
  • Light-headedness
  • Feeling cold when they’re hot to touch
  • Abdominal cramps
  • Headaches
  • Muscle cramps
  • Loss of appetite
  • Vomiting
  • Irritability or confusion
  • Dark-coloured urine

How long does it usually last?

This all depends on how severe the exhaustion was, the temperature outside, and how quickly the affected person rehydrated after getting out of the sun.

If intense symptoms haven’t improved as they start to rehydrate and leave the sun, seek medical advice and attention. If the fatigue and tiredness haven’t worn off completely after 48 hours, it’s best to consult a professional too, just in case.

How serious can it be?

Heat exhaustion should never be ignored as it can ultimately develop into heat stroke.

Severe dehydration can damage and impair kidney function, affect blood pressure, and cause electrolyte imbalances that cause complications like kidney stones and acute internal injury.

It’s important to recognise that certain vulnerable groups like the elderly, people with chronic illnesses, and young children are more susceptible to complications when temperatures rise. This could be because they’re not able to prepare themselves adequately, or because they already find drinking enough water difficult.

For people in these groups, heat exhaustion can quickly become a medical emergency. Make sure to keep them out of the sun and monitor their fluid levels during a heatwave or on particularly hot days.

How common is it?

Heat exhaustion is very common, especially during the summer. It can have a widespread effect on the workplace and public health during the summer, as incidence rates and hospital admissions naturally go up as we all struggle to deal with the heat.

During heatwaves, Public Health England and the Met Office typically issue periodic heat-health alerts. They also report on the increase in hospital admissions and ambulance callouts for heat-related illnesses that typically occur.

Regional ambulance services may also report spikes in calls related to heat-related illnesses when a heatwave strikes. This is likely due to people who are not accustomed to the heat spending too much time in the sun when temperatures start to soar.

The UK Health and Safety Executive (HSE) also publishes advice and guidance for employers. Part of this includes measures to prevent heat exhaustion among workers, especially those working outdoors or in extremely hot or enclosed environments.

Who is most at risk?

Having fun in the sun can make it easy to forget about reapplying sun cream, drinking water regularly, and taking breaks in the shade. The reality is that these simple actions go a long way to preventing the onset of heat exhaustion.

If you’re unprepared during a heatwave, or you’re spending long periods in the sun without breaks, you’re more likely to develop heat exhaustion.

Your risk is also amplified if you’re drinking alcohol. This is because alcohol is a diuretic that makes us urinate more regularly. Using the toilet more often can also cause an electrolyte imbalance that affects our thirst perception and fluid retention.

The more drunk we become, the less likely we are to be vigilant about our health and safety. This is why people passing out and receiving medical attention at festivals is so common.

Places where your risk increases

Hot and humid environments are more likely to cause heat exhaustion.

These include:

  • Beer gardens and pubs
  • Open-air concerts
  • Festivals
  • Gyms
  • Running tracks
  • Urban flats and houses
  • Funfairs
  • Trains and buses
  • Underground transport
  • Factories and warehouses

The right way to avoid it

The best way to treat heat exhaustion is to do everything you can to avoid it in the first place.

If it’s hot and the sun’s out, use the checklist below to make sure you’re prepared:

  • Check the weather forecast
  • Wear lightweight and breathable clothing and a hat if it’s sunny
  • Apply suncream to any exposed areas of skin
  • Pack a bottle of water that you can refill throughout the day
  • Limit your intake of alcohol if you’re out in the sun
  • If you are drinking, make sure you alternate with glasses of water

Advice for the elderly

Encourage older relatives to sip water regularly and to drink before they feel thirsty. You can make this easier by buying them a refillable jug or cup that has measurement markers on the side. This is a great way to help them keep track of their fluid intake and how much they’ve drank throughout the day.

Also, try and limit their intake of caffeinated and alcoholic beverages, as they are a diuretic that makes us urinate more frequently. If they usually drink lots of sugary tea and coffee, satisfy their sweet tooth by swapping these out for a fruit-flavoured squash they like during the summer.

When it gets hot, vulnerable adults should try and stay indoors during the hottest parts of the day. Encourage them to dress for the weather by wearing loose, light-coloured clothing where possible. If things get really hot, try pulling the curtains and getting a fan set up in a dimly lit room to help ease discomfort and lower body temperature.

Advice for parents of young children and babies

Keeping young children safe in the heat is vital because they’re more susceptible to heat than older children and adults. Babies especially should be entirely covered on hot days and kept out of direct sunlight to prevent them from overheating and becoming dehydrated.

Sun exposure

NHS guidance on babies and the sun is as follows:

  • Babies younger than 6 months should be kept out of direct sunlight because their skin doesn’t contain enough melanin
  • Older babies should also be kept out of the sun as much as possible, particularly in the summer and between 11am and 3pm.

If you are taking your baby outdoors, apply a sun cream that is at least SPF 30.

Make sure to reapply their sun cream regularly (especially if they’re in and out of the sea or the paddling pool) and remember to cover areas like their ears, neck, and the backs of their knees.


Keeping your child hydrated is just as important as keeping them safe in the sun. The NHS guidance on keeping children hydrated during the hot weather is as follows:

Babies from 0 to 6 months:

  • Breastfed babies don’t need any additional water until they begin eating solid food
  • When it’s hot, they may want to be breastfed more regularly
  • Their primary source of fluid on a hot day should still come from breast or formula milk
  • If you're bottle feeding, try offering your baby a little cooled boiled water
  • You can also do this during the night if they wake for a feed

Babies around 6 months:

  • Will likely be on some form of solid food
  • Breastmilk or infant formula should remain their primary drink
  • In hot weather, you might need to provide some extra water between meals
  • Offer them sips of water from a cup or beaker
  • You can also do this during the night if they wake for a feed

From 12 months:

  • Water, breast milk, or cow’s milk should be your child’s main fluid source
  • In warmer weather, you can continue to provide extra water between meals
  • Consider frozen lollies made from plain water or very diluted fruit juice
  • Lollies made from diluted juice should only be given at mealtimes to prevent tooth decay.

The best way to treat it

The best thing you can do if you’re feeling dehydrated or tired in the sun is to get into the shade and rehydrate. We’ve expanded on each of these points below.

Get out of the sun

Spending time in the sun accelerates fluid loss because hot environments make us sweat more. If we’re already feeling dehydrated, try to find some shade and rehydrate in a cool environment.

If you spot someone else struggling, do the same and take them to a shaded or air-conditioned area. This will help lower their body temperature and reduce the strain on their internal cooling systems.

If you can, alert someone else so you are both keeping an eye on them and make sure the person has access to plenty of water. Reassure them that they’re okay and that taking some time out to drink some water will quickly improve their condition.


Consistently drinking water is crucial for treating heat exhaustion because water helps regulate our internal temperature.

When we're hot, our body starts to sweat to try and cool us down. This process uses valuable fluids and can cause us to feel dehydrated if we don’t replenish them. Without enough fluid on board, our body can struggle to produce sweat, which can trigger a dangerous rise in our internal temperature.

If you’re exhausted in the heat, try sipping water or an electrolyte-rich drink in the shade. This will help replenish the lost fluid and salt that helps restore our body’s ability to cool itself effectively. Doing this in the shade will also help slow the rate at which you sweat and lose additional fluid.

First aid for heat exhaustion

If you or someone you know is showing signs of heat exhaustion, follow the steps below:

  • Get them into the shade if possible
  • Sit and have a chat to monitor their responsiveness
  • If they’re lightheaded, lay them down and place their feet above their heart
  • Encourage them to slowly sip on a glass of water
  • Cool them from the neck down
  • Do not cool their head – this is counterproductive and can do more harm than good
  • Seek medical assistance immediately if they show any signs of heat stroke

Last updated Wednesday 26 June 2024

First published on Wednesday 26 June 2024