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Heat illness moves fast, and the line between “needs water and shade” and “needs an ambulance” is thinner than most people think. This guide covers heat exhaustion vs. heat stroke: how to tell them apart, what to do for each, and how to avoid both in the first place.
Quick answer
Heat exhaustion: heavy sweating, cool/clammy skin, weakness, nausea — move to shade, cool the body, give water, rest. Heat stroke: body temperature over 103°F, hot/dry or flushed skin, confusion, or loss of consciousness — this is a medical emergency: call 911 and cool the body aggressively while waiting. The single most useful sign to remember: sweating heavily = exhaustion; stopped sweating and confused = stroke.
Heat exhaustion: what it looks like
- Heavy sweating, cool, pale, clammy skin.
- Headache, dizziness, nausea or vomiting.
- Muscle cramps, weakness, fatigue.
- Fast, weak pulse.
- Body temperature usually normal to mildly elevated.
Treating heat exhaustion
- Move to a cool or shaded place immediately.
- Loosen or remove excess clothing.
- Sip water or an electrolyte drink — not large gulps at once.
- Apply cool, wet cloths to the skin, or fan the person.
- Rest lying down with legs slightly elevated.
- If symptoms don’t improve within an hour, vomiting continues, or they worsen, seek medical care — heat exhaustion can progress to heat stroke.
Heat stroke: what it looks like
- Body temperature above 103°F (39.4°C).
- Hot, dry, flushed skin — sweating may have stopped, or skin may feel damp from exertion but with the other signs present.
- Confusion, slurred speech, agitation, or strange behavior.
- Loss of consciousness or seizures.
- Rapid, strong pulse; rapid breathing.
Treating heat stroke — act immediately
- Call 911 right away. Heat stroke can cause organ damage and death; every minute at a dangerously high temperature matters.
- Move to shade or indoors if possible.
- Cool aggressively: ice packs or cold wet cloths at the neck, armpits, and groin (areas with major blood vessels close to the skin); immerse in cold water up to the neck if available (a stream, tub, or trough); fan while wetting the skin.
- Do not give fluids by mouth if the person is confused or unconscious — aspiration risk.
- Keep cooling until emergency help arrives or body temperature clearly drops and symptoms improve.
Who is at higher risk
- Infants, young children, and adults over 65.
- People with heart, lung, or kidney conditions, or who are overweight.
- Certain medications (diuretics, some blood pressure and psychiatric drugs) that affect sweating or hydration.
- Anyone exerting hard in heat without acclimatization — the first hot days of the season, or the first days of a new job/training outdoors, are higher risk.
- Alcohol use increases dehydration risk.
Preventing heat illness
- Hydrate before you’re thirsty — thirst lags behind actual need. Add electrolytes on long, sweaty days.
- Schedule hard activity for cooler hours — early morning or evening.
- Light-colored, loose, breathable clothing and a wide-brim hat.
- Acclimate gradually — the body adapts to heat over 1–2 weeks of repeated exposure.
- Take breaks in shade or AC on hot days; never leave anyone in a parked car.
- Know the heat index, not just the temperature — humidity makes heat far more dangerous by blocking sweat evaporation.
Frequently asked questions
What is the main difference between heat exhaustion and heat stroke?
Heat exhaustion involves heavy sweating with cool, clammy skin and a near-normal temperature, while heat stroke involves a body temperature above 103°F with hot, often dry skin and confusion or altered mental state. Heat stroke is a medical emergency; heat exhaustion usually resolves with rest, cooling, and fluids.
Can heat exhaustion turn into heat stroke?
Yes. Heat exhaustion that isn’t treated, or where the person keeps exerting in the heat, can progress to heat stroke. Watch for confusion, stopped sweating, or symptoms that don’t improve with rest and cooling, and seek medical care if they appear.
What is the fastest way to cool someone with heat stroke?
Cold water immersion up to the neck is the fastest method if available. Otherwise, apply ice packs or cold wet cloths to the neck, armpits, and groin while fanning, and call 911 immediately — cooling should start before and continue during transport.
Should you give water to someone with heat stroke?
Only if they are fully conscious and able to swallow safely. Never give fluids by mouth to someone who is confused, drowsy, or unconscious, due to the risk of choking or aspiration.
How long does it take to recover from heat exhaustion?
With prompt rest, cooling, and fluids, most people improve within 30 minutes to an hour. If symptoms persist beyond that, worsen, or include confusion, treat it as a possible progression to heat stroke and seek medical care.
Who is most at risk of heat stroke?
Infants, adults over 65, people with chronic health conditions, those on certain medications, and anyone doing hard physical activity in heat without being acclimated. Alcohol use and inadequate hydration also raise risk for everyone.
Bottom line
Sweating heavily with cool clammy skin is heat exhaustion — cool down, hydrate, rest. Hot skin with confusion or a very high temperature is heat stroke — call 911 and cool the body aggressively without delay. Prevention (hydration, shade, pacing, acclimatization) is far easier than treating either.
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This article is for general informational purposes only and is not a substitute for professional medical care. Sources: CDC extreme heat and heat-related illness guidance; OSHA heat illness prevention guidance; American Red Cross first aid guidance.