Heat exhaustion and heatstroke
Introduction
Heat exhaustion and heatstroke are two heat-related health conditions. If they're not quickly treated, they can both be very serious.
Heat exhaustion
Heat exhaustion can occur when the temperature inside the body (the core temperature) rises to anything between the normal 37°C (98.6°F) up to 40°C (104°F).
At this temperature, the levels of water and salt in the body begin to fall, which can cause a person to feel sick, feel faint and sweat heavily. Read more about the symptoms of heat exhaustion.
If a person with heat exhaustion is taken quickly to a cool place, is given water to drink and has their excess clothing removed, they should begin to feel better within half an hour and have no long-term complications.
Without treatment, they could develop heatstroke.
Certain groups are more at risk of developing heatstroke or suffering complications from dehydration, and should be taken to hospital. This includes:
- children under two years old
- very elderly people
- people with kidney, heart or circulation problems
- people with diabetes who use insulin
Read more about treating heat exhaustion.
Heatstroke
Heatstroke is far more serious than heat exhaustion. It occurs when the body can no longer cool itself and starts to overheat.
When the core temperature rises above 40°C (104°F) the cells inside the body begin to break down and important parts of the body stop working.
If left untreated, it can lead to complications, such as organ failure and brain damage. Some people die from heatstroke.
The symptoms of heatstroke can include:
- mental confusion
- rapid shallow breathing (hyperventilation)
- loss of consciousness
Read more about the symptoms of heatstroke.
What to do
Heatstroke is a medical emergency and should be treated immediately. Dial 999 to request an ambulance if you suspect heatstroke.
While you're waiting for an ambulance to arrive, make sure that the person is as cool as possible. Move them to a cool area as quickly as possible, remove excess clothing and try to cool them by fanning them. If they're conscious, give them cool, not cold, water to drink.
Read more about treating heatstroke.
Who's at risk?
Heatstroke can affect anyone, but some people are more at risk than others and should take extra precautions during warm weather, especially during a heatwave. These include:
- the elderly
- babies and young children
- people with conditions that affect the body's ability to cool down, such as diabetes
- those who have drunk too much alcohol (which dehydrates the body)
- people on certain drugs and medications, such as antipsychotics and betablockers
- people who might find it difficult to keep cool during a heatwave – for example, those who are bed-bound or disabled.
Read more about the causes of heat stroke.
Avoiding heat exhaustion and heatstroke
There are steps you can take to reduce the risk of heat exhaustion and heatstroke during a heatwave:
- Stay out of the sun during the hottest parts of the day, particularly between 11am and 3pm.
- If you have to go out in the heat, walk in the shade, apply sunscreen and wear a hat.
- Don't leave anyone in a parked car.
- Avoid extreme physical exertion.
- Have plenty of cold drinks, but avoid drinks that contain caffeine and alcohol.
- Eat cold foods, particularly salads and fruit with a high water content.
- Take a cool shower, bath or body wash.
- Sprinkle water over your skin or clothing, or keep a damp cloth on the back of your neck.
- Keep your environment cool.
Read more about preventing heatstroke.
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Symptoms
Heat exhaustion
The symptoms of heat exhaustion can develop rapidly. They include:
- very hot skin that feels ‘flushed’
- heavy sweating
- dizziness
- extreme tiredness (fatigue)
- feeling sick (nausea)
- being sick (vomiting)
- a rapid heartbeat
- mental confusion
- urinating less often and much darker urine than usual
A person with heat exhaustion should be moved quickly to somewhere cool and given fluids (preferably water) to drink. They should then begin to feel better within half an hour.
However, certain groups are more at risk of developing heatstroke or suffering complications from dehydration, and should be taken to hospital. This includes:
- children under two years old
- very elderly people
- people with kidney, heart or circulation problems
- people with diabetes who use insulin
Read more about treating heat exhaustion.
Heatstroke
The symptoms of heatstroke can develop over several days in vulnerable people, such as the elderly and those with long-term health problems, particularly in warm weather.
The symptoms of heatstroke develop more quickly when associated with physical activity. This type of heatstroke is referred to as exertional heatstroke. It usually affects young, active people.
Symptoms of heatstroke include:
- high body temperature – a temperature of 40°C (104°F) or above is often a major sign of heatstroke, although it can be diagnosed at lower temperatures and some people can reach these temperatures during physical exercise without developing heat exhaustion or heatstroke
- heavy sweating that suddenly stops – if the body is unable to produce any more sweat, it's a major warning sign that it has become over-heated and dehydrated
- a rapid heartbeat
- rapid breathing (hyperventilation)
- muscle cramps
The extreme heat that causes heatstroke also affects the nervous system, which can cause other symptoms such as:
- mental confusion
- lack of co-ordination
- fits (seizures)
- restlessness or anxiety
- problems understanding or speaking to others
- seeing or hearing things that aren't real (hallucinations)
- loss of consciousness
Heatstroke is a medical emergency. Dial 999 immediately to request an ambulance if you think that you or someone you know has heatstroke.
While waiting for the ambulance to arrive, move the person somewhere cool and give them fluids to drink (preferably water). You could also cool their skin with water by placing a damp flannel or sheet on them or spraying them gently.
It's better to wait for medical supervision before immersing someone fully in water because it could increase their blood pressure significantly (hypertensive response), which could be dangerous for those with cardiovascular disease or those at risk of stroke, such as the elderly.
Read more about treating heatstroke.
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Causes
Heatstroke occurs when the body is no longer able to cool itself and starts to overheat.
The human body can maintain a stable body temperature in a wide range of different environments. This is known as thermoregulation.
How the body cools itself
There are four ways that the body can cool itself. These are:
- radiation – heat radiates out of the body in the same way as it radiates out of a fire
- convection – cold air or water that crosses the skin cools the body
- conduction – a cooler object that's in direct contact with the skin draws out or conducts heat from the body
- evaporation – the body produces sweat that cools on the skin, lowering the body’s temperature
Normal skin temperature is 32-34°C (89.6-93.2°F). If the outside temperature is higher than your skin temperature, the only way that your body can cool itself is through sweating. Therefore, anything that reduces the amount of sweat that's produced by your body can cause it to overheat. Examples include:
- dehydration – the normal water content of your body is reduced
- wearing tight-fighting clothing
- very hot and humid weather which doesn't allow the sweat to cool
Types of heatstroke
There are two types of heatstroke. They are:
- classic heatstroke
- exertional heatstroke
Classic heatstroke usually affects the elderly, babies and people with chronic (long-term) health conditions. It develops during unusually hot weather, such as during a heatwave.
Exertional heatstroke usually affects young, active people while they're doing strenuous, physical activity for a prolonged period of time in hot conditions. For example, cases of exertional heatstroke can affect:
- athletes
- military personnel
- fire-fighters
Vulnerable groups
Sweat is controlled by a part of the brain called the hypothalamus. The hypothalamus acts like a thermostat that tells the body to produce more sweat when it detects that it's getting hotter.
However, in some elderly people and people with long-term health problems, such as diabetes, the hypothalamus doesn't work as well as it should, putting these groups at increased risk of getting heat exhaustion and heatstroke.
Older women are thought to have a slightly higher risk of heatstroke than older men. This is because women have fewer sweat glands than men and older women are more likely to live alone without immediate help available.
Babies and young children are also at risk as they sweat less and are more affected by dehydration.
People who are unable to keep cool during a heatwave are also more at risk of getting heatstroke. This group may include:
- people with Alzheimer’s disease – a group of symptoms that are associated with a decline in mental abilities, such as memory and reasoning
- people with a disability
- people who are bed-bound
- those who have had too much alcohol
- babies and young children
Drugs and medications
There are a number of drugs and medications that can interfere with the body’s ability to regulate temperature. It puts those who use them at more risk of developing heat exhaustion and heatstroke. These include:
- amphetamines – stimulants such as speed and crystal meth
- cocaine
- antipsychotics – these are used to help treat mental health conditions such as schizophrenia
- benzodiazepines – a type of tranquiliser
- beta-blockers and calcium-channel blockers – these are used to treat high blood pressure (hypertension) and some types of heart disease
- diuretics – used to reduce the amount of fluid in your body
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Diagnosis
Heat exhaustion and heatstroke can be diagnosed by assessing your symptoms and taking your temperature.
A temperature of 40°C (104°F) or above is often a major sign of heatstroke, although it can be diagnosed at lower temperatures, and some people can reach these temperatures during physical exercise without developing heat exhaustion or heatstroke.
Read more about the symptoms of heatstroke.
Further testing
If you have heatstroke, further tests may be recommended to determine whether your body has experienced any additional damage. These tests may include:
- a blood test to check the state of your liver or to see whether damage to your nervous system has led to gases and acids being released into your blood
- urine test – to see if your kidneys have been damaged
- imaging tests, such as a MRI scan or CT scan to see whether any other organs have been damaged
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Treatment
Heat exhaustion
If you suspect that someone has heat exhaustion, follow the advice outlined below.
- Get them to rest in a cool place – ideally a room with air conditioning or, if this isn't possible, somewhere in the shade.
- Get them to drink fluids – this should be water or a rehydration drink, such as a sports drink; they should stop taking fluid on board once their symptoms have greatly decreased (usually within two to three hours).
- Avoid alcohol or caffeine as these can increase levels of dehydration.
- Cool their skin with cold water – if available, use a cool shower or bath to cool them down, otherwise apply a cool, wet flannel or facecloth to their skin.
- Loosen clothing and ensure that the person gets plenty of ventilation.
Dial 999 to request an ambulance if the person doesn't respond to the above treatment within 30 minutes.
If the person is more at risk of developing heatstroke or suffering complications from dehydration then they should be taken to hospital either way. This group includes
- children under two years old
- very elderly people
- people with kidney heart or circulation problems
- people with diabetes who use insulin
Heatstroke
Always call an ambulance in cases of suspected heatstroke.
First aid
While you're waiting for the ambulance to arrive you should do the following:
- Move the person to a cool area as quickly as possible.
- Increase ventilation by opening windows or using a fan.
- If they're conscious, give them water to drink but don't give them medication, such as aspirin or paracetamol.
- Shower their skin with cool, but not cold, water (15-18°C).
- Alternatively, cover their body with cool, damp towels or sheets, or immerse them in cool but not cold water.
- It's better to wait for medical supervision before fully immersing them in water, such as in a bath, as the body’s response could cause them harm.
- Gently massage their skin to encourage circulation.
- If they start to have a seizure (fit), move nearby objects out of the way to prevent injury (don't use force or put anything in their mouth).
- If the person is unconscious and vomiting, move them into the recovery position by turning them on their side and making sure that their airways are clear.
Hospital treatment
After a person has been admitted to hospital, the most important treatment goal is to lower their temperature as quickly as possible. This can be done in two ways:
- immersing their body in an ice-bath
- spraying their body with a mist of cool water while warm air is fanned over the body; the combination of cool water and warm air encourages rapid heat loss through evaporation
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Prevention
In the UK, cases of heat exhaustion and heatstroke usually only occur during periods of unusually hot weather, such as a heatwave. The risk may be greater when travelling abroad in hot countries.
At home
The government operates Heat-Health Watch, which is a system of four different warning levels based on the expected temperatures. This can be useful when planning activities or preparing for a heatwave.
The Welsh Government's heatwave plan 2010 has advice on how to cope during a heatwave, including recommendations for preventing heat-related illnesses. The main recommendations are outlined below.
Stay out of the heat
Stay out of the sun during the hottest parts of the day, particularly between 11am and 3pm. However, it's important to remember that it can also be very hot before and after these times.
If you have to go out in the heat, make sure that you walk in the shade, apply sunscreen and wear a hat and light scarf.
Cool yourself down
Have plenty of cold drinks, but avoid drinks that contain caffeine and alcohol. Try and eat cold foods such as salad and fruit, which have a high water content.
Spraying water on your skin or placing a damp cloth on the back of your neck will help you cool down. You could also take a cool bath or shower.
Keep your environment cool
Place a thermometer in your main living room and bedroom to keep a check on the temperature. If possible, move into a cooler room, particularly for sleeping.
Keep windows that are exposed to the sun closed during the day. Open windows at night when the temperature has dropped. Consider replacing metal blinds or dark curtains as they absorb heat.
Have your loft and cavity walls insulated; this keeps the heat in when it's cold and keeps it out when it's hot. Use pale, reflective external paints.
Turn off non-essential lights and electrical equipment because they generate heat.
Grow trees and leafy plants near windows to act as natural air conditioners. Bowls of water in the house also cool the air through evaporation.
Look out for others
Keep an eye on isolated, elderly, ill or very young people. Make sure that they're able to keep cool. Ensure that they're not left alone in stationary cars during a heatwave.
Check on elderly or sick neighbours and elderly family members or friends every day if possible.
Be alert and call a doctor or social services if someone is unwell or further help is needed.
Travelling abroad
The advice above also applies if you're travelling abroad in a hot country.
It's important to remember that it takes the body 7 to 10 days to acclimatise to a hotter environment. Until that time, you will sweat less than you should. Drink water regularly, avoid staying in the heat too long and wear loose, light clothing.
Athletes should acclimatise for three to four days before undertaking anything but light physical activity, gradually building up activity levels over a two to three-week period.
Alcohol is also an important factor to consider when travelling abroad. Drinking too much alcohol can affect your ability to judge temperature and move to somewhere cooler. It can also contribute to dehydration, increasing the risk of heat exhaustion and heatstroke.
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