Heat exhaustion occurs when a person can't sweat enough to cool the body. It generally develops when a person is working or exercising in hot weather.
Symptoms of heat exhaustion include fatigue, weakness, headache, dizziness, or nausea, and the skin is pale, cool, and moist. Mild heat exhaustion does not cause a change in a person's mental alertness and usually can be treated at home.
Moderate to severe heat exhaustion can sometimes lead to heatstroke, which requires emergency treatment.