Mayo Clinic Health Library

Heatstroke

Updated: 04-03-2012

Heatstroke is the most severe of heat-related problems, after heat cramps and heat exhaustion. Heatstroke often results from exercise or heavy work in hot environments combined with inadequate fluid intake.

Young children, older adults, people who are obese and people born with an impaired ability to sweat are at high risk of heatstroke. Other risk factors include dehydration, alcohol use, cardiovascular disease and certain medications.

What makes heatstroke severe and potentially life-threatening is that the body's normal mechanisms for dealing with heat stress, such as sweating and temperature control, become inadequate. The main sign of heatstroke is a markedly elevated body temperature — generally greater than 104 F (40 C) — with changes in mental status ranging from personality changes to confusion and coma. Skin may be hot and dry — although if heatstroke is caused by exertion, the skin may be moist.

Other signs and symptoms may include:

  • Rapid heartbeat
  • Rapid and shallow breathing
  • Elevated or lowered blood pressure
  • Cessation of sweating
  • Irritability, confusion or unconsciousness
  • Feeling dizzy or lightheaded
  • Headache
  • Nausea
  • Fainting, which may be the first sign in older adults

If you suspect heatstroke:

  • Move the person out of the sun and into a shady or air-conditioned space.
  • Call 911 or emergency medical help.
  • Cool the person by covering with damp sheets or by spraying with cool water. Direct air onto the person with a fan or newspaper.
  • Have the person drink cool water or other nonalcoholic beverage without caffeine, if he or she is able.

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