What Is Heat Stroke?

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Heat stroke is a medical emergency that can occur as a result of extreme heat exposure. It can cause a person to become confused and pass out. Heat stroke is typically sudden, worsens quickly, and may lead to a coma, irreversible brain damage, and death.

Three workers sunbathing during their lunchtime
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Heat stroke can affect anyone, but there are some circumstances when it is more likely. For example, children, people who are disabled, or pets left in a hot car are particularly susceptible to it. Recognizing the condition and calling for emergency medical care can save the life of someone who is experiencing heat stroke.

Awareness and prevention are the most effective ways to avoid the consequences of this condition.

Heat Stroke Symptoms

Heat stroke can be preceded by heat exhaustion, which is characterized by sweating, hot body temperature, dry mouth and skin, dizziness, and lightheadedness. Heat exhaustion can worsen suddenly and quickly, leading to heat stroke, which includes the following symptoms:

  • Flushing
  • Rapid breathing
  • Rapid heartbeat
  • Confusion, disorientation
  • Loss of consciousness
  • Convulsions or seizures (some cases)

With heat stroke, body temperature is usually very high and can rise as high as 104 degrees F or higher.

If you experience or witness heat stroke, you might or might not see early signs. Given this, it is best not to ignore any unusual symptoms or behavior.

If you experience heat stroke, you might feel faint before the symptoms progress, or it can come on suddenly.

If you observe someone having heat stroke, they might act incoherently at first, or they may be very quiet as the condition develops.


Your body functions best at a temperature of 98 degrees F. At hotter or colder body temperatures, the proteins in the body can begin to denature (change shape) and cease functioning as they should. This leads to physical dysfunction and to the symptoms of heat exhaustion and heat stroke.

Anyone exposed to high temperatures or whose body temperature reaches a dangerously high level can suffer from heat stroke. In general, an environmental temperature (indoors or outdoors) near 100 degrees F poses a risk.

Risk Factors

Some people are more susceptible to heat stroke than others, and may not be able to tolerate high temperatures for long. They include:

  • Very young babies
  • Small children
  • Elderly adults
  • Someone who is very sick with an infection or systemic illness (such as cancer, kidney failure, or endocrine disease)
  • Anyone who has a weakened or underdeveloped central nervous system, which is what helps the body regulate changes in temperature
  • People who have difficulty staying hydrated due to difficulty eating and drinking or severe vomiting

Certain situations can make it difficult for anyone to escape from the heat, putting them at risk for heat stroke simply because of their circumstance:

  • Disability that prevents one from leaving a very hot space
  • Living quarters with a lack of fresh air and/or air conditioning
  • Jobs requiring physical, outdoor labor

Athletes who run or exercise in the heat for long periods of time, especially without hydrating, must also be concerned about the potential of heat stroke.

There are also some medications that can affect a person's response to heat and their ability to stay hydrated. These include:

  • Vasoconstrictors, which narrow blood vessels
  • Diuretics, which reduce sodium and water in the body)
  • Beta-blockers, often found in blood pressure medications
  • Some antidepressants and antipsychotic medications


The difference between heat stroke and heat exhaustion is that the symptoms and long-term effects of heat stroke are more severe than those of heat exhaustion. However, the progression from heat exhaustion to heat stroke can be rapid and does not follow a predictable timeline or path.

The diagnostic evaluation of heat stroke includes urgent measurements of vital signs, such as blood pressure, pulse, and respiratory rate. These tests guide the medical team in emergency treatment.

Once a person is stabilized, further tests may include blood tests, urine tests, and imaging examinations. Blood tests and urine tests can help in evaluating dehydration and electrolyte problems, which must be treated with intravenous (IV) fluids.

Imaging tests such as brain magnetic resonance imaging (MRI) and computerized tomography (CT) can identify areas of damage in the brain, kidneys, or gastrointestinal system.

Despite the similar-sounding name, a heat stroke is not the same as the kind of stroke that affects the brain. However, a heat stroke and a brain stroke can both cause loss of consciousness, are both medical emergencies, and may result in permanent brain damage or death.


If you experience or witness the signs of heat exhaustion or heat stroke, you need to call for emergency help right away. In the meantime, try to get indoors or at least some shade, cool the body (with an icepack), and drink cold water (if the person can sit or stand and voluntarily drink without choking). If you have a fan, try to run it close by.

Be careful when caring for someone with heat stroke. If the environment is hot enough for someone else to get overheated, then it may be hot enough for you to become overheated as well. Be sure to stay cool while you are waiting for emergency help to arrive.

Once a person with heat stroke is in medical care, treatment is focused on maintaining optimal body temperature, hydration, and supporting heart and respiratory function. If long-term physical damage has occurred, then rehabilitation may be necessary.

A Word From Verywell

Heat stroke is a preventable emergency. Awareness of the risk factors and signs of heat stroke goes a long way. Anyone can experience it, and caution and attention to the dangers of excessive heat can prevent a tragedy from occurring.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Warning Signs and Symptoms of Heat-Related Illness.

  2. Centers for Disease Control and Prevention. Frequently Asked Questions (FAQ) About Extreme Heat.

  3. Adams WM. Exertional Heat Stroke within Secondary School Athletics. Curr Sports Med Rep. 2019;18(4):149-153. doi:10.1249/JSR.0000000000000585

  4. Gauer R, Meyers BK. Heat-Related Illnesses. Am Fam Physician. 2019;99(8):482-489.

Additional Reading

By Rod Brouhard, EMT-P
Rod Brouhard is an emergency medical technician paramedic (EMT-P), journalist, educator, and advocate for emergency medical service providers and patients.