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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?
• Who is at risk of heat-related illness?
• What are the symptoms of 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.