Heat exhaustion and heatstroke: a case-based approach

The case: unwell in the heat

During a heatwave, a person spends the afternoon outdoors and starts to feel dizzy, sick, and drained. They are sweating heavily, have a headache and cramps, feel very thirsty, and their skin looks pale and clammy. They are still alert and able to talk. This is a typical picture of heat exhaustion, which happens when the body loses too much water and salt through sweating and becomes overheated. It is a warning sign that the body is struggling to cope with the heat. Handled promptly, most people recover within about 30 minutes. But if it is ignored and the person keeps overheating, heat exhaustion can progress to heatstroke, which is far more dangerous. Recognising the early signs and acting quickly is what stops things getting worse.

First aid for heat exhaustion

The aim is to cool the person down and help them rehydrate. Move them to a cool place, ideally somewhere shaded or air-conditioned, and get them to lie down with their feet slightly raised. Remove any unnecessary clothing and cool their skin — for example with cool water on the skin, a fan, or cool packs wrapped in a cloth placed under the armpits or on the neck. Encourage them to sip plenty of fluids; water is fine, and a rehydration drink can help replace lost salts. Stay with them and keep cooling. Most people start to feel better within half an hour. If they do not improve within 30 minutes, or they get worse, treat it as an emergency and call 999. Do not leave someone with heat exhaustion alone until they have recovered.

Heatstroke: a 999 emergency

Heatstroke is different from and much more serious than heat exhaustion. It happens when the body can no longer cool itself and the core temperature climbs dangerously high. The key warning signs are confusion, loss of coordination, or unusual behaviour; skin that feels hot and may be dry (the person may stop sweating); a very high temperature; fast breathing or a pounding heart; a seizure; or loss of consciousness. Unlike heat exhaustion, the person often is not thinking clearly. Heatstroke can damage the brain and other organs and can be fatal, so it is a medical emergency — phone 999 straight away. While waiting for help, move them somewhere cool, remove outer clothing, and cool them actively with water and fanning. Do not give fluids to anyone who is drowsy or not fully alert.

Who is most at risk

Anyone can overheat, but some people are more vulnerable and need extra care in hot weather. These include older people, babies and young children, people with long-term conditions such as heart or lung disease, diabetes, or kidney problems, and those who are very physically active, such as outdoor workers and athletes. Some medicines and drinking alcohol can also make it harder for the body to cope with heat. Babies and older people may not be able to tell you they are struggling, so watch them closely. High humidity makes overheating more likely because sweat does not evaporate as well. During hot spells, checking on elderly neighbours and relatives, and never leaving anyone — especially a child or a pet — in a parked car, can prevent serious harm.

Staying safe in hot weather

Most heat illness is preventable. During hot weather, drink plenty of fluids and avoid excess alcohol, keep out of the sun during the hottest part of the day (usually late morning to mid-afternoon), and stay in the shade where possible. Wear light, loose clothing and a hat, and use sunscreen. Keep your home cool by closing curtains on sunny windows and opening up when it is cooler. Take cool showers and splash your skin with water. Avoid strenuous exercise in the heat, and if you must be active, take frequent breaks and drink regularly. Never leave people or pets in parked cars, which heat up quickly to dangerous levels. Following heat-health alerts and checking on vulnerable friends, relatives, and neighbours helps keep everyone safe when temperatures rise.