Heat Stroke vs Heat Exhaustion: How to Tell the Difference in 30 Seconds
Both look similar to a bystander, but heat stroke kills in under an hour without cooling. The single symptom that distinguishes them, and what to do for each.
Heat exhaustion and heat stroke are the same condition at different severities. Heat exhaustion is the body still trying to cool itself but losing. Heat stroke is the cooling system failed.
The clinical distinction is core body temperature. Heat exhaustion: core temp 100 to 103 F. Heat stroke: core temp above 104 F. Without a rectal thermometer (the only accurate way to read core temp in the field), you cannot measure this directly. So you go by the proxy symptoms.
Heat exhaustion symptoms: heavy sweating, pale skin, weakness, dizziness, nausea, headache, fast pulse, low blood pressure. The person is uncomfortable but lucid. Their skin is cool and damp.
Heat stroke symptoms: skin hot to the touch and either very dry or still profusely sweating, confusion or slurred speech, rapid pulse, body temperature above 104 F if measurable, possible loss of consciousness, possible seizure. The mental status change is the key signal, if the person is confused about their name, where they are, or what is happening, treat it as heat stroke.
The 30-second test: can the person hold a normal conversation? Can they tell you their name, the date, and where they are? If yes, this is heat exhaustion. If no, or if they are slurring, agitated, or confused, this is heat stroke. Call 911 immediately.
What to do for heat exhaustion: move to shade or AC, remove excess clothing, give cool water in sips, apply cool wet cloths to neck, wrists, and groin. Most cases improve in 20 to 30 minutes. If symptoms do not improve or worsen, call 911.
What to do for heat stroke: call 911 first, then cool aggressively while waiting. Ice water immersion is the gold standard if available (lower the person into a tub of ice water up to the neck). If not available, ice packs on neck, armpits, and groin, cool wet sheets over the body, and a fan blowing across the wet sheets. Do not give water, confused people can aspirate.
The difference between survival and death in heat stroke is the speed of cooling. Studies on military trainees and marathon runners show survival rates near 100% if core temp is reduced below 102 F within 30 minutes of collapse. Delay beyond 30 minutes drops survival sharply. Do not wait for the ambulance to start cooling.
Two populations to watch closely: elderly people taking diuretics (their cooling response is weaker), and young athletes during the first two weeks of preseason practice (they have not acclimatized yet). Both groups account for most heat stroke deaths.