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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

Signs and symptoms of heat-related illness vary based on the condition.

• Heat rash symptoms: red bumps on the skin, a feeling of prickly or itchy feeling to the skin.
• Heat syncope symptoms:  dizziness or lightheadedness and fainting, generally due to prolonged exposure to heat, dehydration, or orthostatic hypotension.
• Heat cramps symptoms: significant sweating, involuntary spasm of the large muscles in the body (such as the thigh muscles).
• Heat exhaustion symptoms: nausea and vomiting, headache, muscle cramps, weakness, and profuse sweating.
• Heat stroke symptoms: dizziness, muscle cramps and aches, vomiting, nausea, fatigue, headache, and weakness. Heat stroke is a medical emergency.

Heat stroke is a medical emergency requiring immediate medical attention. It is the most severe form of heat-related illness, and it can sometimes lead to death or permanent disability. Heat stroke occurs when the body's ability to regulate its internal temperature has failed. The body's temperature rises rapidly in excess of 105 F (40.5 C), leading to damage to the brain and other vital organs. Generally, the extent of injury depends on the duration of exposure to excessive heat and the peak temperature attained. Heat stroke is sometimes referred to as sunstroke.

Heat stroke can be categorized as either exertional heat stroke (EHS) or nonexertional heat stroke (NEHS). Exertional heat stroke generally occurs in young, healthy individuals who engage in strenuous activity in hot weather. Nonexertional heat stroke (also referred to as classic heat stroke) typically occurs in the elderly, the very young, or the chronically ill.

Warning signs of heat stroke vary but may include:

• high body temperature (above 104 F or 40 C),
• skin that is red, hot, and either moist or dry (sweating may have stopped),
• rapid heart rate,
• difficulty breathing,
• headache, 
• dizziness,
• loss of coordination,
• nausea and vomiting,
• confusion and restlessness,
• seizures, and
• unconsciousness/coma.

If you see any of these signs, you may be dealing with a life-threatening emergency. Have someone call for immediate medical assistance while you begin cooling the affected individual:

• Get the person to a cool indoor or outdoor area and remove restrictive clothing.
• Cool the person rapidly using whatever methods you can. For example, if possible, immerse the person in a tub of cool water or place them in a cool shower. You may also spray them with lukewarm water and blow cool air from a fan towards them. If the humidity is low, loosely wrap the person in a cool, wet sheet and fan him or her vigorously. Alternatively, place ice or cold packs to the armpits, neck, and groin areas.
• Monitor body temperature, and continue cooling efforts until the body temperature drops to about 102 F or lower (38.8 C), in order to prevent overcooling the affected individual.
• If emergency medical personnel are delayed, call the hospital emergency room for further instructions.
• If the affected individual is awake and alert, give them cool fluids to drink. Do not give them alcohol to drink.

Sometimes the affected individual's muscles will begin to twitch uncontrollably (seizure) as a result of heat stroke. If this happens, try to keep the individual from injuring themself, but do not place any object in the mouth and do not give fluids. If there is vomiting, make sure the airway remains open by turning the person on their to prevent choking.