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Heat-Related Illnesses - Topic Overview

A healthy body temperature is maintained by the nervous system camera.gif. As the body temperature increases, the body tries to maintain its normal temperature by transferring heat. Sweating and blood flow to the skin (thermoregulation) help us keep our bodies cool. A heat-related illness occurs when our bodies can no longer transfer enough heat to keep us cool.

A high body temperature (hyperthermia) can develop rapidly in extremely hot environments, such as when a child is left in a car in the summer heat. Hot temperatures can also build up in small spaces where the ventilation is poor, such as attics or boiler rooms. People working in these environments may quickly develop hyperthermia.

High temperature caused by a fever is different from a high body temperature caused by a heat-related illness. A fever is the body's normal reaction to infection and other conditions, both minor and serious. Heat-related illnesses produce a high body temperature because the body cannot transfer heat effectively or because external heat gain is excessive.

Heat-related illnesses include:

  • Heat rash (prickly heat), which occurs when the sweat ducts to the skin become blocked or swell, causing discomfort and itching.
  • Heat cramps, which occur in muscles after exercise because sweating causes the body to lose water, salt, and minerals (electrolytes).
  • Heat edema (swelling camera.gif) in the legs and hands, which can occur when you sit or stand for a long time in a hot environment.
  • Heat tetany (hyperventilation and heat stress), which is usually caused by short periods of stress in a hot environment.
  • Heat syncope (fainting), which occurs from low blood pressure when heat causes the blood vessels to expand (dilate) and body fluids move into the legs because of gravity.
  • Heat exhaustion (heat prostration), which generally develops when a person is working or exercising in hot weather and does not drink enough liquids to replace those lost liquids.
  • Heatstroke (sunstroke), which occurs when the body fails to regulate its own temperature and body temperature continues to rise, often to 105 °F (40.6 °C) or higher. Heatstroke is a medical emergency. Even with immediate treatment, it can be life-threatening or cause serious long-term problems.
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