Heat exhaustion and heatstroke: the difference, the signs, and when to call 999

What is the difference between heat exhaustion and heatstroke?

Heat exhaustion happens when the body struggles to cope with heat. Heatstroke is the more serious form, and the NHS treats it as an emergency.

NHS inform says heat exhaustion can progress to heatstroke if a person cannot cool down. The NHS says heat exhaustion usually improves once the person cools down within 30 minutes, and NHS inform describes it as usually getting better 30 to 60 minutes after cooling. Someone who has heatstroke, NHS inform says, is treated in hospital.

What are the signs of heat exhaustion?

The NHS lists tiredness, dizziness, headache, feeling sick or being sick, and heavy sweating. The skin can become pale and clammy, and there can be cramps and a high temperature.

For children, the British Red Cross describes dizziness or confusion, headaches or cramps, sweating with cooler skin, a paler colour than usual, nausea, and fast breathing and heart rate. Its advice is to get medical advice even if the child seems to recover, and to call 999 if the child gets worse.

What helps heat exhaustion?

For heat exhaustion the NHS describes moving the person somewhere cool and taking off unnecessary clothing. It also describes giving plenty of water, or an isotonic sports drink or rehydration powder. The skin can be cooled by spraying or sponging with cool water and fanning. Cold packs wrapped in a cloth, placed under the armpits or on the neck, are also described. The NHS says to stay with the person until they are better.

The British Red Cross notes that babies under 6 months do not need to be offered water and may need to feed more often instead.

What are the signs of heatstroke and what happens next?

The NHS lists a very high temperature, and hot skin that is not sweating, among the warning signs of heatstroke. Others are fast breathing, a fast heartbeat, confusion, restlessness, a seizure (fit) and loss of consciousness. The NHS notes that redness can be harder to see on brown or black skin.

If heatstroke is suspected, the NHS says to call 999. It also says not to drive to A&E, and that the 999 call handler will advise what to do. The NHS also says to call 999 if someone with heat exhaustion has not begun to improve after 30 minutes of resting in a cool place, being cooled down and drinking fluids.

What is done while waiting for help?

The NHS describes cooling the person while waiting for the ambulance. This can mean wrapping them in a cool, wet sheet, fanning them, or sponging them with cold water. If the person loses consciousness, the NHS describes putting them in the recovery position. It also describes checking breathing and pulse and starting CPR if there is no sign of life.

For children, the British Red Cross likewise describes calling 999 straight away for heatstroke, moving the child somewhere cool and carrying on cooling while waiting for help.

Who is at higher risk, and how can people stay cool?

GOV.UK describes older people, babies and young children, and people with long-term conditions as more vulnerable in hot weather. Conditions named include heart, breathing and kidney problems and diabetes.

NHS Specialist Pharmacy Service guidance says some medicines may reduce sweating and affect the body's ability to control temperature, which can raise the risk of heat exhaustion and heatstroke. For staying cool, GOV.UK describes closing curtains or blinds on rooms facing the sun, and opening windows at night when it is cooler outside. It also describes planning activity for early morning or evening, drinking plenty of fluids, and limiting alcohol. Never leave babies, children, older people or pets alone in a parked car, the guidance says. Checking on vulnerable neighbours, friends and relatives is also advised.