Hyperthermia is an abnormally high body temperature. Also called heat illnesses, there are several forms of hyperthermia. Heat cramps are fairly mild, whereas heat exhaustion is more severe. Heatstroke is the most serious form of hyperthermia and can be life-threatening.


What is hyperthermia?

Hyperthermia is an abnormally high body temperature — or overheating. It's the opposite of hypothermia, when your body is too cold. Hyperthermia occurs when your body absorbs or generates more heat than it can release. A human’s normal body temperature is about 98.6 degrees Fahrenheit. Any body temperature above 99 or 100 degrees Fahrenheit is too warm.

Hyperthermia is usually the result of overexertion in hot, humid conditions. Most forms of hyperthermia are preventable.


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Is hyperthermia the same as a fever?

Hyperthermia isn’t the same as a fever. When you have hyperthermia, your body temperature rises above a certain “set-point” that’s controlled by your hypothalamus (a part of your brain that controls many body functions). But when you have a fever, your hypothalamus actually increases your body’s set-point temperature. This intentional rise in body temperature is your body’s attempt to fight off an illness or infection.

Are there different types of hyperthermia?

Hyperthermia describes a group of heat illnesses that include (from least to most severe):

  • Heat cramps: Muscle cramps can occur if you lose a lot of electrolytes (salts and other important substances in your body fluids) through sweating. Heat cramps often occur in your arms, hands, lower legs and feet.
  • Heat exhaustion: Heat exhaustion is more serious than heat cramps. Your body temperature may be as high as 104 degrees Fahrenheit. Heat exhaustion can lead to heatstroke.
  • Heat rash: If you sweat a lot in hot, humid weather, you might develop a skin irritation called heat rash. It looks like a cluster of small, red pimples or blisters. Heat rash usually develops in your elbow crease, under your breasts, near your groin or on your upper chest and neck.
  • Heat stress: Occupational heat stress can occur if you have a job that requires you to work in hot conditions. Examples include firefighters, miners and construction workers. Heat stress can lead to heat exhaustion or heatstroke.
  • Heatstroke: The most severe form of hyperthermia is heatstroke. It’s a life-threatening condition that causes your body temperature to rise above 104 degrees Fahrenheit. It causes problems in your brain and other organs. Heatstroke is especially dangerous if your body temperature rises above 106 degrees Fahrenheit.


What is malignant hyperthermia?

Malignant hyperthermia is a genetic condition that can make you susceptible to hyperthermia if you receive a specific combination of sedatives and anesthesia for medical procedures. If you have this disease, your body temperature can spike dangerously during or after surgery. People with malignant hyperthermia might have a reaction the first time they’re exposed to certain medications, but it’s more common after several exposures.

Who gets hyperthermia?

Anyone can get a heat illness, but you’re at especially high risk if you:

  • Are dehydrated.
  • Are over 65 or under 4 years old.
  • Do strenuous physical activity in hot weather.
  • Excessively consume alcohol.
  • Have an electrolyte imbalance.
  • Have certain diseases that affect your ability to sweat, such as cystic fibrosis.
  • Have certain medical conditions, such as problems with your heart, lungs, kidneys, liver, thyroid or blood vessels, are overweight or underweight.
  • Take certain medications, such as diuretics, stimulants, sedatives, tranquilizers or heart and blood pressure.
  • Wear heavy or tight clothing in hot weather.


How common is hyperthermia?

Between 2004 and 2018, an average of 702 heat-related deaths occurred in the U.S. each year. Athletes, outdoor laborers, military trainees, infants and the elderly are the most likely to develop hyperthermia.

Symptoms and Causes

Symptoms of hyperthermia and heat exhaustion.
Heat exhaustion is a type of hyperthermia characterized by blurred vision, dizziness, low blood pressure and other symptoms.

What causes hyperthermia?

Hyperthermia occurs when your body takes in more heat than it releases. Sweat is your body’s natural cooling mechanism, but sometimes sweating isn’t sufficient to keep your body at a normal temperature. When this happens, your body temperature can rise. Physical exertion in very hot, humid weather is the most common cause of hyperthermia.

What are the symptoms of hyperthermia?

Heat cramps typically cause sudden muscle spasms in your feet, calves, thighs, hands or arms. The cramps might feel painful or tense. Your muscles might be sore after the cramp passes.

Symptoms of heat exhaustion include:

Symptoms of heatstroke can often be similar to those of heat exhaustion, but may also include:

People with heatstroke can develop shock, slip into a coma, experience organ failure or die. If you experience symptoms of heat stroke, seek immediate medical attention.

Diagnosis and Tests

How is hyperthermia diagnosed?

Healthcare providers diagnose hyperthermia by reviewing your symptoms, performing a physical exam and taking your temperature. They may also order blood or urine tests.

Management and Treatment

How are heat cramps, heat exhaustion, heat rash and heat stress treated?

If you experience mild-to-moderate heat illness symptoms, you should:

  • Stop physical activity and rest in a cool, well-ventilated environment.
  • Remove heavy or tight clothing.
  • Drink slightly salty beverages to replace lost electrolytes. You can have sports drinks or water with a few teaspoons of salt mixed in. Avoid caffeinated beverages.
  • Apply a cool compress to your skin.
  • Keep irritated skin dry. Apply a powder or ointment to reduce discomfort from a rash.
  • Gently stretch any muscles that are cramping.

You can usually treat these conditions at home. In some cases, your healthcare provider may recommend intravenous (IV) fluid replacement through a catheter in your arm.

How is heatstroke treated?

Heatstroke is a medical emergency that requires treatment in a hospital. If you’re waiting for an ambulance to arrive, try to cool the person as much as possible:

  • Immerse them in cool water, if possible.
  • Mist them with water and blow air across their bodies (evaporative cooling).
  • Apply ice packs to the neck, groin and armpits.
  • Avoid giving any medications, including aspirin and acetaminophen.

At the hospital, you may receive cooled IV fluids. A healthcare provider may also recommend cold-water lavage. This is a procedure that washes out body cavities with cold water.


How can I prevent hyperthermia?

In most cases, it’s possible to prevent hyperthermia. You should:

  • Avoid strenuous physical activity in hot, humid conditions.
  • Consume sports drinks, lightly salted water or broth.
  • Never leave children (or pets) in closed, hot spaces such as cars.
  • Stay in air-conditioned or well-ventilated areas during heat waves.
  • Wear lightweight, loose-fitting and light-colored clothing if you’ll be out in the heat.

If you must do activities in the heat due to your job or a sport, let your body gradually acclimate to the heat. Start doing light work or exercise about two weeks before you need to do the really hard work. Then, gradually build your body’s ability to withstand high temperatures. If possible, plan to do the work during the early morning hours when it might be cooler.

Outlook / Prognosis

What’s the prognosis (outlook) for people with hyperthermia?

Most people recover fully from heat illnesses once they rest in a cool environment and replace lost electrolytes. But heatstroke can lead to permanent organ damage or even death.

Living With

When should I contact my doctor?

Contact your doctor if you or someone else:

  • Has a high fever.
  • Has trouble walking, breathing or speaking.
  • Is sweating excessively.
  • Loses consciousness.
  • Seems confused or disoriented.

A note from Cleveland Clinic

Hyperthermia, or heat illness, is an abnormally high body temperature. It’s usually the result of doing too much physical activity in hot, humid weather. Infants, the elderly, athletes and people with strenuous outdoor occupations are at the highest risk for hyperthermia. Heat illnesses can range from mild (heat cramps or heat exhaustion) to severe (heatstroke). People with a heat illness should cool their body temperature right away. Call 911 immediately at the first signs of heatstroke.

Medically Reviewed

Last reviewed on 11/19/2021.

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