What is heat exhaustion?

Dr. Michael Roizen, MD
Internal Medicine
Heat exhaustion is deadly serious. It's caused by being both overheated and dehydrated.

When you sweat and as perspiration evaporates, your body releases heat, but it's hardly the physical equivalent of central air. Extremely high temperatures can overwhelm your body's cooling mechanism, especially if it's already compromised by lack of fluid (dehydration), obesity, heart disease, sunburn or age extremes -- both the elderly and the very young really suffer. Plus, the combo of high humidity and sizzling temps thwarts evaporation. You still sweat, but it just drips off without cooling you, so you're losing precious fluid as well.

Heat exhaustion occurs when the body cannot sweat enough to cool off the body. Heat exhaustion is usually a result of too much heat and/or humidity and not enough fluids in the body. Working or exercising in hot weather can bring on heat exhaustion.

A person with heat exhaustion is generally experiencing fatigue, weakness, dizziness, or vomiting. The skin can be cool, clammy, pale, red or flushed. A person experiencing heat exhaustion will be aware that he or she is thirsty and needs to cool off.

Moving the person to a cool place out of the sun and giving that person water is an effective way to treat heat exhaustion. Start with a small amount of water, then increase the amount as the person begins to feel better. Having the person lie down can help alleviate the nausea or dizziness. Applying a cool compress or sponge to the body also relieves some of the symptoms.

Heat exhaustion can be prevented by avoiding strenuous activity during the hottest part of the day, drinking a minimum of eight glasses of water a day (more if you are exercising), and wearing light-colored clothing to reflect the sun's rays.

Left untreated, heat exhaustion can lead to heat stroke. Heat stroke requires immediate medical attention.

Heat exhaustion is a milder form of heat-related illness that develops as a result of dehydration. The cardiovascular system becomes overloaded due to water loss, the high demands of muscle for blood flow during activity, and the need to eliminate heat from the body. Those most prone to heat exhaustion are elderly people, those with high blood pressure, and those working or exercising in a hot environment. (This answer provided for NATA by the Marist College Athletic Training Education Program)
Heat exhaustion is a more severe condition than heat cramps.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.