Heatstroke is a life-threatening condition that happens when your body temperature rises above 104 degrees Fahrenheit (40 degrees Celsius). It’s usually the result of overexertion in hot, humid conditions. Symptoms can include confusion, seizures or loss of consciousness. Untreated, heatstroke can lead to organ failure, a coma or death.


What is heatstroke?

Heatstroke is a life-threatening condition that causes your body to overheat. It’s defined as a body temperature above 104 degrees Fahrenheit (40 degrees Celsius). Heatstroke, also called sunstroke, is the most severe form of hyperthermia, or heat-related illness. Heatstroke can lead to brain damage, organ failure or death.


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Are there different types of heatstroke?

There are two types of heatstroke:

  • Exertional heatstroke: This form of heatstroke is usually the result of physical overexertion in hot, humid conditions. It can develop in a few hours.
  • Non-exertional heatstroke: Also called classic heatstroke, this type can occur due to age or underlying health conditions. It tends to develop over several days.

Are heat exhaustion and heatstroke the same thing?

Heat exhaustion and heatstroke are both types of hyperthermia. Heat exhaustion can develop into heatstroke if left untreated. But heat exhaustion isn’t as severe as heatstroke, doesn’t cause neurological problems and usually isn’t life-threatening.


Who gets heatstroke?

Anyone can get heatstroke. But infants and the elderly are at especially high risk because their bodies may not be able to regulate temperature effectively. Athletes, soldiers and people with occupations that require physical labor in hot environments are also susceptible to heatstroke.

Other factors that increase your risk of heatstroke include:

  • Drinking alcohol.
  • Being male.
  • Being dehydrated.
  • Drugs that affect your body’s ability to regulate temperature, such as diuretics, sedatives, tranquilizers, or heart and blood pressure medications.
  • Having certain diseases that affect your ability to sweat, such as cystic fibrosis.
  • Having certain medical conditions, such as a sleep disorder or problems with your heart, lungs, kidneys, liver, thyroid or blood vessels.
  • Wearing heavy or tight clothing, such as protective gear.
  • Having a high fever.
  • Having obesity.
  • A past history of heatstroke.
  • Poor physical conditioning or not being used to hot conditions.

How common is heatstroke?

Studies suggest that heatstroke occurs in about 20 out of 100,000 people each year in the U.S. It’s most common in urban areas during periods of very hot weather. Heatstroke causes between 240 and 833 deaths in the U.S. annually.


Symptoms and Causes

What causes heatstroke?

Heatstroke occurs when your body can’t cool itself down. Your hypothalamus (a part of your brain that controls many bodily functions) sets your core body temperature. It typically sets your temperature at about 98.6 degrees Fahrenheit (37 degrees Celsius). But if your body takes in more heat than it releases, your internal temperature rises above this set-point.

What are the signs and symptoms of heatstroke?

Heatstroke is a medical emergency. If you or someone you know exhibits any of the following signs or symptoms, call 911 immediately:

  • Anhidrosis (dry skin that doesn’t sweat, which is more common in non-exertional heatstroke).
  • Ataxia (problems with movement and coordination).
  • Balance problems.
  • Delirium (confusion or disorientation).
  • Dizziness.
  • Excessive sweating that continues after you’ve stopped exercising (more common in exertional heatstroke).
  • Hot, flushed skin or very pale skin.
  • Low or high blood pressure.
  • Lung crackles (bubbling or gurgling sound in the lungs).
  • Nausea and vomiting.
  • Oliguria (low urine output).
  • Rapid breathing or tachycardia (fast heart rate).
  • Seizures.
  • Syncope (fainting) or loss of consciousness.
  • Weakness.

What are the potential complications of heatstroke?

People with heatstroke can develop shock or slip into a coma. High body temperature can lead to:

Diagnosis and Tests

How is heatstroke diagnosed?

Healthcare providers typically diagnose heatstroke in the emergency department. They review your symptoms, perform a physical exam and take your temperature. They may also order blood tests or urinalysis. Additional tests might include a chest X-ray or electrocardiogram (EKG) to monitor the electrical activity in your heart.

Management and Treatment

How is heatstroke treated?

Heatstroke requires immediate medical treatment. If you’re waiting for an ambulance to arrive, try to cool the person as much as possible by:

  • Applying ice packs to the neck, groin and armpits.
  • Encouraging them to drink slightly salted fluids, such as sports drinks or salted water.
  • Having them lay down in a cool, shady, well-ventilated environment.
  • Immersing them in cool water, if possible.
  • Misting them with water and blowing air across their bodies (evaporative cooling).
  • Monitoring their breathing carefully and removing any airway blockages.
  • Not giving any medications, including aspirin and acetaminophen.
  • Removing any clothing that is tight or heavy.

At the hospital, the person with heatstroke may receive:

  • Cooled intravenous fluids through a vein in their arm.
  • Cooling blanket.
  • Ice bath.
  • Medication to prevent seizures.
  • Supplemental oxygen.

Sometimes cold-water lavage is necessary. This treatment uses catheters (thin, flexible tubes) to fill body cavities with cold water. This helps lower the body temperature overall. The catheter may go into the rectum or down the throat.

Healthcare providers stop cooling treatments once the body reaches about 102 degrees Fahrenheit (38.9 degrees Celsius). The length of time you stay in the hospital depends on the severity of your heatstroke and how well your organs are functioning.


How can I prevent heatstroke?

In most cases, it’s possible to prevent heatstroke by:

  • Avoiding strenuous physical activity in hot, humid conditions.
  • Consuming sports drinks, lightly salted water or broth.
  • Gradually letting your body acclimate to warm temperatures over several weeks if you’ll have to be in hot conditions for work or sports.
  • Never leaving children (or pets) in closed, hot spaces such as cars.
  • Staying in air-conditioned or well-ventilated areas during heat waves.
  • Wearing lightweight, light-colored and loose-fitting clothing if you’ll be out in the heat.

Outlook / Prognosis

What’s the prognosis (outlook) for people who’ve had heatstroke?

Your outlook after heatstroke depends on a variety of factors, including:

  • Age.
  • How high your body temperature spiked.
  • How long your body temperature stayed high before you received treatment.
  • Overall health.

Between 10 and 65% of people with non-exertional heatstroke die from the illness. The outlook is better for exertional heatstroke, which has a mortality rate of 3 to 5%. Some people experience permanent organ damage or neurological dysfunction.

During your recovery after heatstroke, you can expect changes in your body temperature for several weeks. You should avoid physical activity for at least a week. You will also need periodic tests to monitor your kidney and liver function. Even temporary complications of heatstroke can take several months to go away.

After you’ve had heatstroke once, you’re more likely to get this heat illness again. Take preventive measures any time you plan to be in hot conditions.

Living With

When should I contact my doctor?

If you’ve had heatstroke and are recovering, contact your doctor right away if you experience anything abnormal such as:

  • Cognitive dysfunction (problems thinking or remembering).
  • Difficulty breathing.
  • Liver or kidney problems.
  • Low urine output.

A note from Cleveland Clinic

Heatstroke is a life-threatening condition that occurs when your body temperature gets too high. It’s usually the result of overexertion in hot, humid weather. Symptoms may include confusion, seizures or loss of consciousness, among others. If you or someone you know has heatstroke, seek immediate medical attention and try to lower the person’s body temperature as quickly as possible.

Medically Reviewed

Last reviewed on 09/13/2021.

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