Heat Illness

What is heat illness?

Heat illness happens when your body gets overheated, usually when you are active in very hot or humid weather. Heat illnesses include heat cramps, heat exhaustion, and heatstroke, the most serious type of heat illness. You are at high risk for heat illness if you:

  • Are an older adult
  • Are overweight
  • Have heart disease
  • Have high blood pressure or a chronic illness
  • Work in a hot place

The medical term for heat illness is hyperthermia.

What is the cause?

Heat illness usually happens after long exposure to hot temperatures. It can also be caused by being sick with a high fever or exercising too hard. Overdressing, eating too much, not drinking enough fluids, or drinking too much alcohol can make it more likely that you will get overheated.

When your body gets hot, it has ways of cooling itself. For example, when you sweat, the moisture on your skin evaporates and cools your skin. When the temperature is too hot or when there is too much humidity, sweating may no longer cool your body enough to keep your temperature from rising too high.

What are the symptoms?

As your body gets hotter and is unable to cool down, your symptoms will get worse. First, you may lose too much fluid and have heat cramps. Without treatment, your symptoms can get worse and you may have heat exhaustion or heatstroke.

Symptoms may include:

Heat cramps:

  • Muscle cramps, most often in your belly, arm, or leg muscles
  • Muscles that feel hard and tense
  • Mild swelling of your feet or hands
  • A red, raised rash called heat rash or prickly heat

Heat exhaustion:

  • Dizziness
  • Weakness
  • Nausea or vomiting
  • Confusion
  • Muscle cramps
  • Headaches
  • Heavy sweating


  • Little sweating or urination
  • Confusion or loss of consciousness
  • Shortness of breath
  • Nervousness
  • Seizures
  • Coma

Heatstroke is a life-threatening condition in which your body temperature rises quickly to 104°F (40°C) or higher and your body’s ability to control your temperature breaks down. Heatstroke may cause damage to your kidneys, heart, lungs, muscles, liver, intestines, and brain.

How is it treated?

To treat heat cramps stop the activity, drink a lot of fluids, and massage and stretch cramped muscles. Heat cramps may get better more quickly if you drink a sports drink that contains salt and other electrolytes rather than just plain water.

The treatment of heat exhaustion depends on what symptoms you have and how bad they are. It’s important to treat heat exhaustion right away to keep symptoms from getting worse. You may need to do some or all of the following:

  • Stop exercising or any other activity. Loosen your clothing.
  • Get out of the sun and go into a cool place, preferably with air conditioning.
  • Cool your body with a fan, spray, cool moist washcloth, or cool bath or shower.
  • Drink plenty of cool water, clear juice, or a sports drink. Don’t drink iced drinks or alcohol. Heat cramps may get better more quickly if you drink a sports drink that contains salt and other electrolytes rather than just plain water.
  • Massage and stretch cramping muscles.
  • Lie down and rest.

Get medical attention if the symptoms get worse or last longer. You may need to stay out of the heat and avoid strenuous activity for a few days if you have heat exhaustion.

Heatstroke is an emergency and needs to be treated at the hospital. Follow the treatment for heat exhaustion until medical help arrives.

How can I help prevent heat illness?

  • Avoid strenuous activity in hot or humid weather.
  • Stay out of the hot sun.
  • Wear a hat if you are working or exercising in the sun, and wear light-colored, loose fitting clothing in hot weather.
  • Take time to get used to a new climate. If you are not used to the heat, expose yourself to it briefly at first and increase your time in the heat slowly.
  • Drink plenty of water whenever you spend a lot of time in the sun or in a hot place. Drink extra water when you sweat, even if you are not thirsty. If you are on a diet that limits your fluids or if you take diuretic medicine (water pills), you may need to be careful about how much you drink. Talk to your healthcare provider about this.
  • Open windows or use a fan or air conditioner to improve airflow. Try to keep at least 1 room in your home cool. Keep windows covered with curtains, shades, or blinds during the hottest part of the day. Set air conditioners below 80°F (27°C).
  • If your home stays very hot, visit friends or family in cooler homes. During a heat wave, check with your city’s emergency services to find out where there are cool buildings you can go to. For example, you might visit air-conditioned places such as libraries, shopping malls, and theaters.
  • Eat smaller, lighter meals and limit how much alcohol you drink when it is very hot or when you are not used to a hot climate.
  • If you take medicines, talk to your healthcare provider to see if any of your medicines make it more likely that you will have problems in the heat.
Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth.
Last modified: 2014-04-04
Last reviewed: 2014-03-30
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright ©1986-2015 McKesson Corporation and/or one of its subsidiaries. All rights reserved.

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