Heatstroke generally occurs when an individual has been too hot for too long, whether working, exercising, or simply sitting in a hot environment.

Also known as sunstroke, heatstroke is a serious condition and must be considered an emergency.

If left untreated, damage to internal organs can occur. The longer it is left, the more serious heatstroke can become. In some cases, heatstroke can be fatal.1

According to the Centers for Disease Control and Prevention (CDC), heatstroke caused 7,415 deaths in the United States between 1999 and 2010.2

In this article, MNT Knowledge Center will look at the symptoms, causes and treatments of heatstroke, as well as the possible long-term effects of heatstroke and how to prevent it from occurring.

Fast facts on heatstroke

Here are some key points about heatstroke. More detail and supporting information is in the main article.

  • Heatstroke is a serious condition and can be fatal. Symptoms include dizziness, mental changes, and nausea.
  • If the body temperature rises above 40° Celsius, and the body loses the ability to cool down, it is considered to be heatstroke.
  • Some people are more susceptible to heatstroke, including young people, older adults and overweight individuals
  • Heatstroke can be brought on by physical exertion in hot conditions, or simply by being in a hot environment
  • Treating heatstroke centers around bringing body temperature down
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Heatstroke can affect anyone of any age.

If someone becomes too hot and loses water and salt from the body, leading to tiredness, weakness and muscle cramps, this is referred to as heat exhaustion.

If the body loses the ability to maintain the correct temperature and it becomes dangerously high, this is referred to as heatstroke.3

The symptoms of heatstroke can include:

  • High body temperature: An elevated body temperature is the main characteristic of heatstroke.
  • Mental changes: These can include confusion, seizures (particularly in children), delirium, slurred speech, irritability, and coma.
  • Sweat changes: In heatstroke brought on by hot weather, the skin will feel hot and dry. Heatstroke induced by physical exertion will leave the skin feeling moist.
  • Nausea: This is feeling of being sick or needing to vomit.
  • Headache: A throbbing headache is common with heatstroke.
  • Color change: The skin may turn red as the body becomes hotter.
  • Breathing: Breathing might become quicker and shallower.
  • Heart rate: As the body attempts to cool down, the heart is put under increasing strain causing heart rate to rise.
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Individuals with heatstroke must have their internal temperature reduced as rapidly as possible.

The main aim of treating heatstroke is to lower the patient’s temperature and prevent further damage.

There are a number of potential ways to achieve this, including:

  • Immersion: The person with heatstroke is submerged in cold water or an ice bath.
  • Evaporation cooling: Cold water is misted onto the skin while warm air is fanned onto the body. This causes evaporation, which cools the skin.
  • Cooling blankets and ice packs: Cooling blankets are wrapped around the individual with heatstroke. Ice packs are placed in regions where large veins come close to the surface of the skin, such as the groin, armpit, neck, and back. This ensures that the temperature of the blood rapidly decreases.
  • Muscle relaxants: Drugs, such as benzodiazepines, may be given if the body temperature is not dropping. These prevent the body from shivering in response to the cold treatments.

Heatstroke is a serious condition, and professional medical help must be sought immediately.

While waiting for help, the individual should go somewhere less warm and attempt to reduce their temperature with damp sheets, a cold bath, or cooling drinks. Alcohol must be avoided.


Medical professionals can usually diagnose heatstroke from a person’s appearance and a discussion about their recent history.

Medical tests will sometimes be ordered to rule out other potential causes. Such tests might include:

  • Blood test: This measures gas levels, as well as potassium and sodium in the blood, to check for damage to the central nervous system (CNS).
  • Urine test: This checks kidney function. Darker urine is a sign that the patient has a heat-related condition.
  • Muscle test: This confirms whether any damage has been done to the muscle tissue.
  • X-rays: These can investigate any damage to the internal organs.

The major causes of heatstroke are categorized into two types.

    Exertional heatstroke

    This refers to heatstroke caused by intense activity in a hot environment, whether exercise or work.

    Exertional heatstroke is more likely to occur if an individual is not used to high temperatures. Heat-related medical emergencies during sports events are estimated to be ten times more prevalent than cardiac-related occurrences.4

      Nonexertional or classic heatstroke

      This type is caused by exposure to a particularly hot environment. Classic heatstroke is most likely to occur if exposed to humid conditions for long periods of time. Those who are already sick are more susceptible, as are older people.

        In both cases, the effects of heatstroke can be exacerbated by wearing too much clothing, not replacing water lost to sweating and by drinking alcohol, which can affect the body’s temperature regulation.

        Although high summer temperatures are rarely considered a health threat, in the US, they kill more people than hurricanes, tornadoes, floods, and lightning combined. As a result, they should be treated with caution.7

        Heatstroke is a potentially life-threatening condition, but it is avoidable. Remaining cool and hydrated is essential. Below are some simple ways in which this can be achieved:

        • Clothing: Wear loose-fitting, lightweight clothes. These allow the body to cool properly
        • Fluids: Maintain fluid intake to replace fluids lost through sweating
        • Parked cars: Never leave someone in a car, as this is a common cause of heatstroke in children. In a sealed car, the temperature can rise almost 7° Celsius in 10 minutes. Even if the windows are cracked, and the car is in the shade, it is still not safe. Between 1998 and 2011, at least 500 children in the U.S. died from being left inside hot cars, with 75 people dying at under 2 years of age.8
        • Timing: Take extra precautions during the hottest parts of the day, between 11 am and 3 pm. If it is not possible to cease activity, increase fluid intake and take frequent rests in the shade.
        • Sunburn: Avoid being sunburned as this affects the way in which the body cools down. Wear a wide-brimmed hat and use sunscreen.
        • Caution: If an individual is at risk of heatstroke, whether due to medications, health status, or age, they should ensure medical services are nearby if they plan to partake in strenuous activity on a hot day.

        Heatstroke is an underestimated condition that is completely avoidable if simple recommendations are followed.

        To summarize: On a hot day, wear loose clothes and have a cold drink while you sit calmly in the shade.

        It was initially believed that recovery from heatstroke, even if prolonged, would normally be complete with no long-term physical deficits. After the 1995 heatwave in Chicago, it was discovered that this is not necessarily the case.

        During the heatwave, more than 600 people died in just 9 days, and more than 3,000 more were taken to the emergency department. A research team followed 58 near-death cases of heatstroke to assess any long-term loss in function.

        The researchers found that almost half of the participants died within a year. 21 percent died before being discharged from hospital, and another 28 percent died after release.

        One-third of those who survived had a “moderate to severe functional impairment” that was not relieved after 12 months.6

        Anyone can have heatstroke, but some groups are more susceptible than others. Factors that increase the likelihood of heatstroke include the following.

        Exertion in high temperatures: Anyone who is likely to be involved in intense activity in high temperatures is at risk. This commonly includes military personnel and sportspeople.

        Age: The CNS is responsible for monitoring and maintaining the correct internal temperature. In young children, the CNS is not yet formed, and once a person is over 65 years of age, the CNS slowly deteriorates. Young children and older adults are therefore most at risk of heatstroke.

        Medications: Some medications can increase the risk of heatstroke by interfering with either the way the body responds to heat or by limiting the ability to stay hydrated.

        The following drugs can increase the risk:

        • vasoconstrictors, or drugs that narrow blood vessels
        • beta-blockers, or medications that block adrenaline to regulate blood pressure
        • diuretics, or drugs that rid the body of sodium and water
        • antidepressants and antipsychotics

        Sudden exposure: Heatstroke is more likely to occur at the beginning of a heat wave or when visiting a much hotter climate.

          Sleep deprivation: There is some evidence that being deprived of sleep can increase the chances of heatstroke.5

            Medical conditions: Some ailments can increase the risk of heatstroke. These include heart and lung disease, obesity, a sedentary lifestyle, gastroenteritis, and a history of heatstroke.

              Depending on how long body temperature is elevated for, heatstroke can result in different complications. If body temperature is not reduced quickly, organs can swell and become damaged, which can be permanent.

              If treatment is not found quickly, heatstroke can be fatal.