Heat Exhaustion

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Slideshow: Understand the Risks and Signs of Dehydration

What causes heat exhaustion?

Heat exhaustion occurs when a person exercises and works in a hot environment and the body cannot cool itself adequately. Dehydration occurs with water loss from excessive sweating, which causes muscle cramps, weakness, and nausea and vomiting. This makes it difficult to drink enough fluid to replenish the body's water supply, and the lack of body water impairs further sweating, evaporation and cooling.

Relative humidity is an important factor in developing heat exhaustion. If the humidity is too high, sweat on the skin cannot evaporate into the surrounding air and body temperature cooling fails.

Living in a hot environment may predispose a person to heat exhaustion. During a heat wave, the elderly, the poor, and those who live an isolated life may not have access to air conditioning and are at risk of heat-related illnesses.

Who is at risk for heat exhaustion?

Heat exhaustion usually affects people who are working or exercising in a hot environment. Those at risk for heat exhaustion include:

  • Infants and young children are at risk because their temperature regulation mechanisms are not fully developed. They also are dependent upon others for water and appropriate clothing.
  • The elderly are similarly at risk because of underlying medical conditions that limit the ability to sweat including poor circulation, skin changes, and chronic medication usage.
  • Socioeconomic issues increase the risk of heat exhaustion if access to air conditioning is limited. During heat waves, large cities often open cooling centers to help minimize the risk of large numbers of people succumbing to heat-related illness.
  • Certain medications such as antidepressants, antipsychotics, and tranquilizers may impair the ability of the body to sweat.
  • Alcohol consumption
  • The overweight or obese

The body has the ability to acclimate to hot weather but if heat waves come suddenly, or if a person travels from a cooler environment to a hot environment, the risk of heat exhaustion increases. It takes about 7 to 10 days for the body to adapt to hot weather. A non-acclimated person can produce a liter or almost a quart of sweat in an hour to assist in cooling the body. A person who is acclimated to the heat can produce 2 or 3 liters of sweat per hour, doubling or tripling the cooling potential for the body.

Medically Reviewed by a Doctor on 6/18/2015

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