Heat exhaustion is excessive loss of salts (electrolytes) and fluids due to heat, leading to decreased blood volume that causes many symptoms, sometimes including fainting or collapse.

Heat exhaustion is more severe than heat cramps. Fluids and salts are more depleted, and symptoms are more severe.

Symptoms and Diagnosis

Dizziness, light-headedness, weakness, fatigue, headache, blurred vision, muscle aches, or nausea and vomiting may develop. Muscle cramps may occur but often do not. People may feel faint or even lose consciousness when standing. Drenching sweats are common. Mild confusion may develop. The heart rate and breathing rate may become rapid. Blood pressure may become low. Body temperature is usually normal and if it is high, it is not higher than 104° F (40° C).

Heat exhaustion usually is diagnosed on the basis of the symptoms and occurrence after exposure to heat.

Treatment

Treatment involves replacing fluids and salts, usually intravenously, and removing people from the hot environment. Removing or loosening clothing and applying wet cloths or ice packs to the skin also aid cooling.

After receiving fluids, people usually recover rapidly and fully. If left untreated, heat exhaustion can lead to heatstroke.

Last full review/revision February 2009 by James P. Knochel, MD