Quick answer

What is heat exhaustion and heatstroke?

Heat exhaustion happens when the body overheats — causing heavy sweating, dizziness, nausea and headache. Move to a cool place, drink fluids, and rest. Heatstroke is an emergency — the body stops cooling itself, skin may be hot and dry, and confusion or collapse can follow. Call 999 for heatstroke or if heat exhaustion does not improve within 30 minutes.

Hot weather can be dangerous

In heatwaves and hot summer days, the body can struggle to cool itself — especially for vulnerable people. Heat exhaustion is overheating with symptoms that usually improve with cooling and fluids. Heatstroke is a life-threatening emergency where the body’s temperature regulation fails. Knowing the difference saves lives.

Heat exhaustion — symptoms

Heat exhaustion develops after prolonged exposure to heat, especially with dehydration or exertion:

  • headache
  • dizziness and confusion
  • nausea and vomiting
  • heavy sweating
  • pale, clammy skin
  • muscle cramps
  • fast breathing and pulse
  • intense thirst
  • weakness and fatigue
  • temperature above 38°C — usually below 40°C

Heat exhaustion is serious but usually reversible with prompt cooling.

What to do for heat exhaustion

  1. Move to a cool place — shade, air-conditioned room, or cool bath
  2. Lie down and raise feet slightly
  3. Remove unnecessary clothing
  4. Cool the skin — fan, cool wet sponges on neck and armpits, cool packs
  5. Drink water or oral rehydration solution — sip slowly
  6. Rest until symptoms improve — usually within 30 minutes

If not improving within 30 minutes, or if vomiting prevents drinking → call 999 (may be progressing to heatstroke).

Heatstroke — a medical emergency

Heatstroke occurs when core body temperature rises above 40°C and the body’s cooling mechanisms fail. It can develop from untreated heat exhaustion or rapidly in extreme heat with exertion.

Call 999 immediately if someone has:

  • hot skin — may be dry OR still sweating (exertional heatstroke in athletes may present with sweating)
  • confusion, agitation, or slurred speech
  • loss of consciousness or collapse
  • seizures
  • not responding normally
  • very high temperature
  • rapid heartbeat

Heatstroke can cause organ damage and death without emergency treatment.

First aid for heatstroke while waiting for ambulance

  • move to coolest available place
  • remove outer clothing
  • cool aggressively — ice packs in armpits and groin, cool wet sheets, fan while wetting skin
  • if conscious, offer sips of cool water
  • do not give aspirin or paracetamol — they do not help heat illness
  • place in recovery position if unconscious but breathing
  • start CPR if not breathing normally

Who is most at risk

  • babies and young children — cannot regulate temperature well
  • older adults — especially over 75, living alone, or with limited mobility
  • chronic illness — heart, lung, kidney disease, diabetes
  • medications — diuretics, antihistamines, beta-blockers, antipsychotics (reduce sweating or thirst)
  • physical exertion in heat — athletes, outdoor workers
  • alcohol — increases dehydration and impairs judgement

Preventing heat illness

  • drink regularly — water, diluted squash; avoid excess alcohol
  • stay indoors during peak heat (11am to 3pm) if vulnerable
  • wear light, loose clothing and a hat
  • use sunscreen — sunburn reduces sweating
  • never leave anyone in a parked car — temperatures rise fatally within minutes
  • check on elderly neighbours and relatives in heatwaves
  • keep bedrooms cool — close curtains, use fans

Heat exhaustion in children

Children overheat faster. Ensure regular drinks, shade, and lighter activity in peak heat. Seek help if a child is floppy, unusually drowsy, not drinking, or not improving after cooling.

After a heat illness episode

See a GP if you do not feel fully recovered within a few days. Repeat episodes suggest need for better prevention strategies — especially if on medicines that increase risk.

If you feel unwell from fluid loss without heat exposure, see guidance on gastroenteritis and oral rehydration. Heat illness specifically relates to environmental temperature overwhelming the body’s cooling capacity.

Common questions

What is the difference between heat exhaustion and heatstroke?
Heat exhaustion — heavy sweating, pale clammy skin, dizziness, nausea, still sweating. Heatstroke — body temperature above 40°C, hot skin (may be dry or still sweating), confusion, collapse, seizures. Heatstroke is a medical emergency — call 999.
What are the symptoms of heat exhaustion?
Headache, dizziness, nausea, heavy sweating, pale clammy skin, cramps, fast pulse, intense thirst, and feeling weak or faint. Core temperature may be raised but usually below 40°C.
How do you treat heat exhaustion?
Move to a cool place, lie down with feet raised, remove unnecessary clothing, cool skin with fans and cool wet sponges on neck and armpits, drink water or oral rehydration solution slowly. Most people improve within 30 minutes.
Who is most at risk in hot weather?
Babies and young children, people over 75, those with heart, lung or kidney disease, diabetes, mobility problems, and people on medicines that reduce sweating (some antihistamines, antipsychotics, diuretics). Athletes and outdoor workers also at risk.
How can I prevent heat illness?
Drink regularly (not just when thirsty), avoid alcohol, stay in shade during peak heat (11am to 3pm), wear light clothing and hat, use sunscreen, and never leave people or pets in parked cars.

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