Heat stroke

Defining heat stroke

overheated woman pouring water over head
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Heat emergencies, Heat illness

Medical Specialties: 

Emergency medicine, Family practice, Internal medicine

Clinical Definition:

Heat stroke is the most severe of three types of heat emergencies, also including heat cramps and heat exhaustion. Heat stroke can cause shock, brain damage, organ failure and death. Fever, irrational behavior and confusion are common.

In Our Own Words:

Heat stroke is the most severe form of heat-related illness and can cause shock, brain damage, organ failure and even death.

It occurs, as the name implies, when temperatures rise. Heat cramps and heat exhaustion are two other less serious heat emergencies. Symptoms of heat stroke include fever above 104 degrees Fahrenheit, dry and red skin, rapid and shallow breathing and irrational behavior.

Heat stroke is usually related to prolonged exertion in a hot environment, but can also occur in elderly or sick people who have problems with body temperature regulation. Heat stroke is a medical emergency, and 911 should be called immediately. While waiting for medical help, first aid is important. The person should lie down in a cool place with feet raised 12 inches. Apply wet, cool cloths to the skin and give fluids until medical help arrives.

A Closer Look at Heat-Related Illness:

Your body is capable of generating a lot of heat. During strenuous exercise, the amount of heat that your body generates can increase by 20 times!

Typically, our bodies get rid of heat by 4 mechanisms:

  • sweating and evaporation of skin moisture
  • radiation of infrared electromagnetic energy into the environment
  • conduction or the direct transfer of heat to a cooler object (like a wet cloth)
  • convection or loss of heat to air currents (think breeze)

These 4 mechanisms of heat loss are regulated by the preoptic nucleus of the anterior hypothalamus, a part of the brain that acts as a central thermostat.

For example, the brain sends out signals for the blood vessels of your body to dilate and thus give off heat.

When you're exposed to too much heat and your body is unable to maintain normal temperature, it overheats (kind of like a car). This overheating results in a spectrum of heat-related disorders, including heat cramps, heat exhaustion, and heat stroke.

Heat cramps refer to involuntary muscle spasms of the skeletal muscle. These cramps usually affect people who are not used to strenuous exercise in a hot and humid environment, like football players on the first day of training camp or a roofer laying shingles on a super-hot day. Heat cramps that present without significant dehydration can be treated by the ingestion of 0.1 percent saline solution or flavored electrolyte solutions like Gatorade. 

Heat exhaustion is more severe than heat cramps and results in a rise in core body temperature. Heat exhaustion is caused by depletion of body sodium and fluids. Of note, people who end up drinking too much water can dilute sodium levels in the blood resulting in heat exhaustion.

Symptoms of heat exhaustion include stomach cramps, confusion, dizziness and malaise. Treatment of heat exhaustion typically occurs in a hospital setting and involves the administration of intravenous fluids and cooling interventions.

Heat stroke occurs when your body becomes completely overwhelmed by heat and can no longer thermoregulate. Specifically, the core body temperature rises past 40.5 degrees Celsius and in addition to symptoms seen with heat exhaustion, other life-threatening symptoms occur like organ damage. This organ damage can affect the liver, kidneys, intestines and heart. Heatstroke is a true medical emergency that requires immediate treatment in a hospital setting.


University of Maryland Medical Center. "Heat emergencies." Medical encyclopedia. January 2012. Accessed November 2013.

Harvard Medical School. "Fluids, cool air key to avoiding heat stroke." Harvard Health Publications. July 2013.

Harvard Medical School. Accessed November 2013.

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