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November 21, 2009
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Hyperthermia and Heat-Related Illness

Medical Author: Steven Doerr, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

What is hyperthermia?

Hyperthermia is overheating of the body. The word is made up of "hyper" (high) + "thermia" from the Greek word "thermes" (heat). Hyperthermia is literally high heat. There are a variety of heat-related illnesses, including heat stroke and heat exhaustion. Other heat-related health problems include heat cramps, heat rash and sunburn.

Summer can bring heat waves with unusually high temperatures that last for days and sometimes weeks. In the summer of 1980, a severe heat wave hit the United States, and nearly 1,700 people lost their lives from heat-related illness. Likewise, in the summer of 2003, tens of thousands of people died of the heat in Europe. High temperatures put people at risk.

What causes hyperthermia and heat-related illnesses?

People suffer heat-related illness when the body's temperature control system is overloaded. The body normally cools itself by sweating. But under some conditions, sweating just isn't enough. In such cases, a person's body temperature rises rapidly. Very high body temperatures can damage the brain or other vital organs.

Several factors affect the body's ability to cool itself during extremely hot weather. When the humidity is high, sweat will not evaporate as quickly, preventing the body from releasing heat quickly. Other conditions that can limit the ability to regulate temperature include old age, obesity, fever, dehydration, heart disease, poor circulation, sunburn, and drug, and alcohol use.

Those at greatest risk of heat-related illness include:

  • infants and children up to four years of age

  • people 65 years of age or older

  • people who are overweight

  • people who overexert during work or exercise

  • people who are ill or on certain medications

Infants and children up to four years of age are very sensitive to the effects of high temperatures and rely on others to regulate their environments and provide adequate liquids.

People 65 years of age or older may not compensate for heat stress efficiently, and are less likely to sense and respond to changes in temperature.

Overweight people may be prone to heat sickness because of their tendency to retain more body heat.

Any health condition that causes dehydration makes the body more susceptible to heat-related illness. If you or someone you know is at higher risk, it is important to drink plenty of fluids, avoid overexertion, and get your doctor or pharmacist's advice about medications being taken for:



Next: Hot weather health emergencies »

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Hyperthermia

What is dehydration?

The majority of the body is made up of water, with up to 75% of the body's weight due to H2O. Most of the water is found within the cells of the body (intracellular space). The rest is found in what is referred to as the extracellular space, which consists of the blood vessels (intravascular space) and the spaces between cells (interstitial space).

Total body water = intracellular space + intravascular space + interstitial space

Dehydration occurs when the amount of water leaving the body is greater than the amount being taken in. The body is very dynamic and always changing. This is especially true with water in the body. We lose water routinely when:

  • we breathe and humidified air leaves the body;
  • we sweat to cool the body; and
  • we urinate or have a bowel movement to rid the body of waste products.

In a normal day, a person has to drink a significant amount...

Read the Dehydration article »










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