What Is Heatstroke?

Heatstroke is a medical emergency that occurs when overexposure to heat overwhelms the body’s internal temperature-regulating mechanisms. Consequently, the protective sweating reflex ceases to function. (Evaporation of sweat on the skin’s surface is one of the primary means for the dissipation of excess heat.) Body temperature subsequently soars to dangerous heights (104°F or above).

Unless emergency medical assistance is obtained promptly, shock, coma, brain damage, kidney failure, or even death may result. Infants and the elderly are at the greatest risk of severe consequences, but heatstroke may occur even in highly trained athletes.

What Causes Heatstroke?

  • Prolonged exposure to hot weather and high humidity
  • Dehydration or insufficient fluid intake
  • Electrolyte disturbances (imbalances in sodium, potassium, calcium, and magnesium)
  • Impaired sweat gland function, which may be present at birth (congenital).
  • Strenuous work or exercise in hot weather.
  • Alcohol and caffeine consumption, as well as overeating, increase risk.
  • Risk is greater among older people (as internal temperature-regulating mechanisms become less responsive with age) and among overweight people (since extra layers of body fat tend to retain heat).
  • Certain medications, including diuretics and antihistamines, may increase risk of heatstroke.
  • Heart disease and diabetes are risk factors.
  • A recent dehydrating illness (one that involved excessive vomiting or diarrhea) increases susceptibility.

Symptoms of Heatstroke

  • Body temperature of over 104°F
  • Headaches, dizziness, giddiness and fatigue
  • Hot, dry, red skin; appears gray in later stages.
  • Conspicuous absence of sweating, despite high body temperature (Profuse sweating may occur initially, then cease as the body’s temperature-regulating mechanisms break down.)
  • Rapid heartbeat
  • Shallow and rapid breathing
  • Nausea and vomiting
  • Muscle cramps
  • Confusion, delirium, or stupor, progressing to seizures or loss of consciousness
  • Sudden tiredness, confusion and irritability

Preventing Heatstroke

  • In hot, humid weather, increase fluid intake, wear light clothing, take frequent cool baths, and try to remain in a cool (preferably air-conditioned) environment. Avoid alcohol, caffeine, and strenuous activity. These recommendations are especially important for the elderly, the chronically ill, or the very young.
  • The body gradually adjusts to hotter climates over a period of one to three weeks. When the weather changes or you travel to warmer environs, spend increasingly longer amounts of time in the heat, followed by periods of rest in cool conditions to promote full acclimatization.
  • Wear a hat or use an umbrella to protect yourself from the sun.
  • Apply sunscreen with a sun protection factor (SPF) of 15 or higher.
  • Plan outdoor activities at cooler times of day, early morning or evening.
  • Monitor weather conditions and pay close attention to temperature and humidity levels indoors and outdoors.

Heatstroke Diagnosis

  • Suspect heatstroke when confusion or altered behavior develops after exposure to a hot environment, especially after exertion.
  • Urine and blood tests may be performed to determine a heatstroke victim’s degree of dehydration.

How to Treat Heatstroke

  • Heatstroke is an emergency: summon professional medical assistance at once.
  • While waiting for emergency help to arrive, move the patient into a shady area or, ideally, a room with air conditioning. Elevate his or her feet. Loosen or remove clothing. Sponge the person with cold water or place in a cool bath. Offer cool liquids only if the person is awake and can drink normally.
  • Professional treatment involves controlled, gradual cooling of the patient, fluid and electrolyte replacement (via oral or intravenous delivery), and sedatives to control seizures if they occur.

When to Call a Doctor

EMERGENCY Call an ambulance if signs of heatstroke develop.


Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference

Simeon Margolis, M.D., Ph.D., Medical Editor

Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 24 Oct 2011

Last Modified: 17 Sep 2015