Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 1998;58(3):759

See related article on heat-related illnesses.

What is heat illness?

When you get warm, your body sweats to cool itself. As it gets warmer, your body must sweat more. As the sweat on your body evaporates (dries up in the breeze), your body gets cooler. If the weather is hot and also humid, your sweat can't evaporate very well. So, as the humidity goes up, your body doesn't cool off as well. This means that your body's internal temperature begins to rise. When you can't sweat enough to cool your body, you might get a heat illness. Heat illness may cause you to feel tired, to have muscles that are weak, tired or cramping, and to have dizziness, nausea, vomiting or headache. Heat cramps, heat exhaustion, heat stroke and sunstroke are different heat illnesses. They occur when your body isn't able to keep itself cool enough.

How can I avoid getting a heat illness?

To decrease your risk of heat illness, follow these tips:

  • Stay in air conditioning if possible.

  • Drink lots of water before, during and after any outdoor activity.

  • Avoid drinks with caffeine or alcohol.

  • Increase the amount of time you spend outdoors every day little by little.

  • Take a lot of rest breaks while outdoors in hot weather.

  • Avoid direct sunlight and stay in the shade when you can.

  • Wear light-colored, loose-fitting, open-weave clothes.

  • Avoid activities that require you to wear a helmet.

  • Try to schedule activities or workouts early in the morning or late in the evening. Avoid heavy outdoor activity between 10 a.m. and 6 p.m., when the sun is hottest.

What should I do if I feel sick in the heat?

If you get symptoms of heat illness, such as cramps, nausea, headache or vomiting, take off as much clothing as possible and wet yourself with cool or lukewarm water. Drink some fluids. Stay in the shade or in air conditioning.

You should see a doctor right away if you become confused, lose consciousness, vomit frequently, stop sweating or stop urinating.

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