By Mayo Clinic Staff

Overview

Heat exhaustion is one of the heat-related syndromes. These syndromes vary in seriousness, ranging from mild to possibly life-threatening. Other types of heat-related illnesses include heat rash, heat cramps, heat syncope and heatstroke.

Heat exhaustion can happen when the body loses too much water or salt — usually because of heavy sweating or dehydration. It can begin suddenly or happen over time, usually after working, exercising or playing in the heat.

When to seek emergency help

Call 911 or your local emergency number if the affected person:

  • Faints.
  • Becomes agitated.
  • Is confused.
  • Has a seizure.
  • Is not able to drink.
  • Has a core body temperature – measured with a rectal thermometer – of 104 degrees Fahrenheit (40 degrees Celsius), which indicates heatstroke.

Symptoms

Heat exhaustion symptoms include:

  • Cool, moist skin with goose bumps when in the heat.
  • Heavy sweating.
  • Faintness.
  • Dizziness.
  • Fatigue.
  • Weak, rapid pulse.
  • Low blood pressure after standing up.
  • Muscle cramps.
  • Nausea or vomiting.
  • Headache.
  • Extreme thirst.
  • Mild confusion.
  • Decreased urine output.

Treatment

Untreated, heat exhaustion can lead to heatstroke, which is a life-threatening condition. If you suspect heat exhaustion, take these steps immediately:

  • Move the person out of the heat and into a shady or air-conditioned place.
  • Lay the person down and raise the legs and feet slightly.
  • Remove tight or heavy clothing.
  • Have the person sip chilled water, a sports drink containing electrolytes or another nonalcoholic beverage without caffeine.
  • Cool the person by spraying or sponging with cool water and fanning.
  • Monitor the person carefully.

Contact a healthcare professional if symptoms get worse or if the person doesn't improve after taking first-aid measures.

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April 16, 2024