Guide · Heat illness first aid

Heat exhaustion vs heatstroke — the symptoms, first aid and when to call 999.

A calm, fact-checked reference summarising NHS guidance on how to tell heat exhaustion from heatstroke, and the five-step response that resolves 90% of cases at home.

Cool cloth and glass of water on a wooden surface, calm daylight
In short

Heat exhaustion — dizziness, heavy sweating, temperature ≥ 38 °C — usually resolves within 30 minutes of cooling and fluids. Heatstroke — temperature ≥ 40 °C, hot dry skin, confusion or unconsciousness — is a medical emergency. Call 999 immediately and keep cooling the person while you wait.

Heat exhaustion

Symptoms — act within 30 minutes.

  • —Tiredness and weakness
  • —Dizziness or feeling faint
  • —Headache
  • —Feeling sick or being sick
  • —Heavy sweating and pale, clammy skin
  • —Muscle cramps in arms, legs or stomach
  • —Fast breathing or fast pulse
  • —Temperature of 38 °C or above
  • —Being very thirsty
Heatstroke

Emergency — call 999 now.

  • —Still feeling unwell after 30 minutes in a cool place
  • —Very high temperature (40 °C or above)
  • —Hot skin that is not sweating and may look red (harder to see on brown or black skin)
  • —Fast heartbeat
  • —Fast breathing or shortness of breath
  • —Confusion, lack of coordination or slurred speech
  • —Seizures (fits)
  • —Loss of consciousness
Five-step first aid

What to do in the first 30 minutes.

  1. 01

    Move them somewhere cool

    Indoors, a shaded outdoor spot, or an air-conditioned car or building. Get them out of direct sun immediately.

  2. 02

    Lie them down, raise their feet slightly

    This helps blood flow back to the brain and reduces dizziness. If they are conscious, keep them lying down for the full 30 minutes.

  3. 03

    Cool the skin fast

    Spray or sponge with cool (not cold) water and fan them. Wet cloths on the neck, armpits, wrists and groin cool blood as it passes through — these are the highest-impact spots.

  4. 04

    Give them water to sip

    Water is best. A sports drink or oral rehydration solution can help replace lost salts if they have been sweating heavily. Avoid alcohol.

  5. 05

    Stay with them for 30 minutes

    If they recover and feel better, they've had heat exhaustion — keep them cool and hydrated for the rest of the day. If they don't recover, or symptoms get worse, this is heatstroke.

Heat illness FAQs

What people ask when someone starts to feel unwell in the heat.

What is the difference between heat exhaustion and heatstroke?
Heat exhaustion is the body's early warning — dizziness, heavy sweating, headache, temperature around 38 °C. It resolves within 30 minutes if the person cools down and drinks fluids. Heatstroke is when the body's temperature-regulation fails — temperature 40 °C or above, hot dry skin, confusion, possible seizures or unconsciousness. Heatstroke is a medical emergency; heat exhaustion usually is not.
When should I call 999 for heat exhaustion?
Call 999 if the person still feels unwell after 30 minutes in a cool place, has a temperature of 40 °C or above, has hot dry skin, is confused, has a seizure, loses consciousness, or is not responsive. Any of these signs means it has become heatstroke and needs emergency treatment.
How long does heat exhaustion take to recover from?
The NHS says most people recover within 30 minutes of getting to a cool place, resting and drinking fluids. If someone hasn't improved in 30 minutes, treat it as heatstroke and call 999 immediately.
Can you have heat exhaustion in the UK?
Yes. UK heatwaves regularly push temperatures above 30 °C, and heat exhaustion and heatstroke are treated in UK A&E departments every summer. UKHSA amber and red Heat-Health Alerts are issued precisely because heat-related illness and death rise sharply at these thresholds.
Who is most at risk of heat exhaustion and heatstroke?
NHS and UKHSA guidance highlight: adults aged 65 and over, babies and young children, people with heart, lung or kidney conditions, people with diabetes, people taking medications that affect sweating or blood pressure, people doing heavy physical work or exercise in the heat, and people who are homeless.
References

Sources for every claim on this page.

Related reading: how to keep cool in a heatwave, employer heat guidance (HSE), AC vs fans.

Not medical advice. This page summarises publicly available NHS, UKHSA and WHO guidance for general information. If you are worried about someone's symptoms, call NHS 111 or 999 in an emergency.

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