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Medical Author:

Steven Doerr, MD

Steven Doerr, MD

Steven Doerr, MD, is a U.S. board-certified Emergency Medicine Physician. Dr. Doerr received his undergraduate degree in Spanish from the University of Colorado at Boulder. He graduated with his Medical Degree from the University Of Colorado Health Sciences Center in Denver, Colorado in 1998 and completed his residency training in Emergency Medicine from Denver Health Medical Center in Denver, Colorado in 2002, where he also served as Chief Resident.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• Heat-related illness facts
• What is a heat-related illness?
• What causes a heat-related illness?
• Heat stroke
• Heat exhaustion
• Heat cramps
• Heat syncope
• Heat rash
• Heat-related illness prevention
• Find a local Doctor in your town
• Hyperthermia Index

People suffer heat-related illness when the body's normal temperature control system is unable to effectively regulate its internal temperature. Normally, at high temperatures the body primarily cools itself through the evaporation of sweat. However, under certain conditions (air temperatures above 95 F or 35 C and with high humidity), this cooling mechanism becomes less effective. When the humidity is high, sweat will not evaporate as quickly, preventing the body from releasing heat quickly. Furthermore, without adequate fluid intake, excessive fluid losses and electrolyte imbalances may also occur leading to dehydration. In such cases, a person's body temperature rises rapidly. Very high body temperatures can damage the brain and other vital organs.

Picture of the layers of the skin including the sweat glands

Other conditions that can limit the ability to regulate body temperature include old age, obesity, fever, dehydration, heart disease, poor circulation, sunburn, and drug or 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 with mental illness, and
• people who are chronically 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 to provide adequate fluid intake. Moreover, they have a higher metabolic rate and inefficient sweating compared to adults.

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. The elderly population also is at a higher risk because they usually have other pre-existing medical conditions, and they often take medications that can make them more vulnerable to dehydration.

Overweight people may be prone to heat-related illness 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:

• high blood pressure,
• depression,
• nervousness,
• mental illness,
• insomnia, or
• poor circulation.