How do I tell heat exhaustion from heatstroke, and what do I do?
The four cooling steps, the thirty-minute rule that separates the two, and the specific signs that mean stop cooling and ring an ambulance.
- Difficulty
- beginner
- Time
- 7 min
- Read
- 4 min
- Safety
- warning
Short answer
Heat exhaustion: tiredness, dizziness, headache, feeling or being sick, heavy sweating, cramps, thirst. Move them somewhere cool, remove unnecessary clothing, give plenty of water or an isotonic drink, and cool the skin by spraying or sponging with cool water and fanning them. They should be better within 30 minutes. If not, or if any heatstroke sign appears, ring 999.
These are two stages of the same process and the distinction is practical rather than academic: one is treated where the person is, and the other is an ambulance. The thirty-minute rule is what separates them for anyone without a thermometer or medical training.
Safety
Step by step
- Recognise heat exhaustion.Tiredness, dizziness, headache, feeling sick or being sick, excessive sweating, cramps in the arms, legs or stomach, a high temperature, intense thirst, and irritability. The person is usually still sweating and still making sense.
- Move them somewhere cool.Indoors, or into shade with moving air. Getting out of direct sun is the first and biggest change you can make.
- Remove unnecessary clothing.Jacket, socks, anything tight or extra. The aim is to let heat leave the skin.
- Give them plenty to drink.Water, or a sports or rehydration drink. Someone who is confused or drowsy should not be given anything to drink — that is a heatstroke sign and it changes what you do.
- Cool the skin actively.Spray or sponge them with cool water and fan them. Cold packs under the armpits or on the neck help. Evaporation is what does most of the work, which is why fanning matters as much as the water.
- Give it thirty minutes.They should start to feel better within half an hour. That is the threshold in the guidance and it is the practical test. No improvement in thirty minutes means ringing 999.
- Know the heatstroke signs.A very high temperature, hot skin that is not sweating, fast breathing or a fast heartbeat, confusion or restlessness, a seizure, or loss of consciousness. Any of these is 999 immediately.
- Keep cooling while you wait.Do not stop because you have called an ambulance. Keep them somewhere cool, keep sponging and fanning, and if they become unresponsive but are breathing, use the recovery position.
Tips
- Sweating stopping is the sign people misread as improvement. Hot, dry skin in someone who was sweating heavily is a heatstroke sign, not a recovery sign.
- Older people, very young children, people with heart or lung conditions and people on certain medicines are at much higher risk, and they often do not complain of feeling hot.
- Never leave anyone — or any animal — in a parked car in warm weather. The interior temperature rises far faster than people expect and a cracked window makes very little difference.
Common mistakes
- Giving a drink to someone who is confused or drowsy — Confusion is a heatstroke sign, and someone whose consciousness is affected cannot reliably protect their airway. They need 999 and cooling, not fluid by mouth.
- Using an ice bath at home — Immersion cooling is used in specific supervised settings. At home it risks a sudden shock response, and the practical, recommended approach is water on the skin plus moving air.
- Assuming someone is fine because they are indoors — Heatstroke in older and vulnerable people frequently happens indoors, in a poorly ventilated room, over a period of days rather than in an hour on a beach.
- Giving alcohol or caffeine to rehydrate — Neither helps and both work against you. Water or an oral rehydration or isotonic drink is what the guidance recommends.
If it doesn't work
They have stopped sweating and their skin is hot and dry
Cause: A heatstroke sign — the body's cooling has failed — Fix: Ring 999 immediately and keep cooling them while you wait. Do not read the absence of sweat as improvement.
They feel better after twenty minutes but are still weak
Cause: Heat exhaustion resolving — Fix: Keep them cool and resting for the remainder of the day, keep the fluids going, and do not return to activity in the heat. Recurrence the same day is common.
Muscle cramps in the legs after exercise in heat
Cause: Heat cramps, an early stage of the same process — Fix: Stop, cool down, rest and rehydrate. Treat it as an early warning rather than a separate minor problem.
Questions people ask
How hot does it have to be?
There is no threshold temperature. Humidity, exertion, clothing, age, medication and how acclimatised someone is all matter, and heat illness happens on days that do not feel extreme.
Can heatstroke happen without sun?
Yes. Exertional heatstroke happens in athletes and workers in the shade, and classic heatstroke happens to vulnerable people indoors during a heatwave.
Is it different for children?
Children heat up faster than adults and are less good at recognising it in themselves. The same actions apply, with a lower threshold for ringing for help.