Heat Stroke vs Heat Exhaustion — Know the Difference

Heat exhaustion: heavy sweating, pale clammy skin, tiredness, dizziness, headache, nausea, cramps, thirst. Move the person somewhere cool, take off extra clothing, give water or a rehydration drink if they are alert and can swallow, and cool the skin: spray or sponge with cool water and fan them, cold packs wrapped in cloth under the armpits or on the neck. Stay with them — they should start to feel better within 30 minutes (NHS, UK).

Heat stroke is an emergency: confusion, strange behaviour or slurred speech, poor coordination, a seizure, a very high temperature, fast breathing. The skin is hot — dry or still sweating: people who collapse during sport or physical work often sweat heavily (CDC, US). Call emergency services — 999 in the UK, 911 in the US, 112 in the EU — and cool the person as fast as you can while you wait: cool water over the body or a cool wet sheet and fanning, ice or cold packs on the neck, armpits and groin (NHS, CDC). Do not give them anything to drink (CDC). If they are unresponsive, check their breathing: breathing normally — put them on their side; not breathing normally (occasional gasps are not breathing) — tell the emergency operator and start CPR (NHS).

Look at the brain, not the sweat. Confusion, strange behaviour or a seizure — or no improvement after 30 minutes of rest and cooling — should be treated as heat stroke, whether or not the person is sweating. Fainting in the heat also needs urgent help: it can be a simpler heat faint (heat syncope, CDC/NIOSH), but only a medic can tell the two apart.