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First Aid and Emergencies

Heat Exhaustion and Heat Stroke

Prevention - Home Treatment - When to Call a Health Professional

Heat exhaustion occurs when your body cannot sweat enough to cool you off. It generally develops when you are working or exercising in hot weather. Symptoms include:

Heat exhaustion can sometimes lead to heat stroke , which requires emergency treatment. Heat stroke happens when you stop sweating and your body temperature continues to rise, often to 40.5°C (105°F) or higher. Symptoms of heat stroke include:


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  • Avoid strenuous physical activity outdoors during the hottest part of the day.

  • Wear light-coloured, loose-fitting clothing to reflect the sun.

  • Avoid sudden changes of temperature. Air out a hot car before getting into it.

  • If you take diuretics, ask your doctor about taking a lower dose during hot weather.

  • Drink 8 to 10 glasses of water per day. Drink even more if you are working or exercising in hot weather.

  • If you exercise strenuously in hot weather, drink more liquid than your thirst seems to require. For example, runners should drink about 0.25 L (1 cup) of water 10 to 15 minutes before running and another 0.25 L (1 cup) of water every 3.2 km (2 mi) or so.

Home Treatment

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  • Get out of the sun to a cool spot, and drink lots of cool water, a little at a time. If you are nauseated or dizzy, lie down.

  • If a person's temperature exceeds 38.9°C (102°F), call for immediate help and try to lower the temperature as quickly as possible:

    • Apply cool (not cold) water to the person's whole body; then fan the person. Or apply ice packs to the groin, neck, and armpits. Do not immerse the person in ice water.

    • If you can get the person's temperature down to 38.9°C (102°F), take care to avoid overcooling. Stop cooling the person once his or her temperature is lowered to 36.9°C (98.6°F).

    • Do not give aspirin or acetaminophen to reduce the temperature.

    • Watch for signs of heat stroke (confusion or unconsciousness; red, hot, dry skin).

    • If the person stops breathing, call for immediate help and start rescue breathing (See Rescue Breathing and CPR).

When to Call a Health Professional

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Call 911 or seek emergency care if the person's body temperature reaches 38.9°C (102°F) and keeps rising, or if signs of heat stroke develop:

  • Confusion, disorientation, unconsciousness.

  • Skin that is red, hot, and dry, even under the armpits.

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