Overview

Heatstroke is a condition caused by the body overheating. This usually happens because of exposure to high temperatures or physical activity in high temperatures for too long. There are a few stages of heat injury, and heatstroke is the most serious. It can happen if body temperature rises to 104 F (40 C) or higher. Heatstroke is most common in the summer months.

Heatstroke needs emergency care. If it's not treated, heatstroke can quickly damage the brain, heart, kidneys and muscles. This damage gets worse the longer treatment is delayed, which increases the risk of serious complications or death.

Symptoms

Heatstroke symptoms include:

  • High body temperature. A core body temperature of 104 degrees Fahrenheit (40 degrees Celsius) or higher is the main sign of heatstroke.
  • Change in mental state or behavior. Confusion, agitation, slurred speech, irritability, delirium, seizures and coma can all result from heatstroke.
  • Change in sweating pattern. In heatstroke brought on by hot weather, skin feels hot and dry to the touch. However, in heatstroke brought on by strenuous exercise, sweating may be profuse.
  • Nausea and vomiting. Someone with heatstroke may feel sick to their stomach or vomit.
  • Flushed skin. Skin may turn red as body temperature increases.
  • Rapid breathing. Breathing may become rapid and shallow.
  • Racing heart rate. Pulse may significantly increase because heat stress places an extreme burden on the heart to help cool the body.
  • Headache. Heatstroke may cause the head to throb.

When to see a doctor

If you think a person may be experiencing heatstroke, seek immediate medical help. Call 911 or your local emergency services number.

Take immediate action to cool the person with heatstroke while waiting for emergency treatment.

  • Get the person into shade or indoors.
  • Remove excess clothing.
  • Cool the person with whatever means available — put in a cool tub of water or a cool shower, spray with a garden hose, sponge with cool water, fan while misting with cool water, or place ice packs or cold, wet towels on the person's head, neck, armpits and groin.

Causes

Heatstroke can happen as a result of:

  • Being in a hot environment. In a type of heatstroke, called nonexertional (classic) heatstroke, being in a hot environment leads to a rise in core body temperature. This type of heatstroke typically happens after exposure to hot, humid weather, especially for a long period of time. It happens most often in older adults and in people with ongoing health conditions.
  • Doing strenuous activity. Exertional heatstroke is caused by an increase in core body temperature brought on by intense physical activity in hot weather. Anyone exercising or working in hot weather can get exertional heatstroke, but it's most likely to happen if you're not used to high temperatures.

In either type of heatstroke, your condition can be brought on by:

  • Wearing heavy clothing that prevents sweat from evaporating easily and cooling the body.
  • Drinking alcohol, which can affect the body's ability to regulate temperature.
  • Becoming dehydrated by not drinking enough water to replenish fluids lost through sweating.

Risk factors

Anyone can develop heatstroke, but several factors increase your risk:

  • Age. The ability to cope with extreme heat depends on the strength of the central nervous system. In the very young, the central nervous system is not fully developed. In adults over 65, the central nervous system becomes less responsive, which makes the body less able to cope with changes in body temperature. Both age groups usually have difficulty remaining hydrated, which also increases risk.
  • Exertion in hot weather. Military training and participating in sports, such as football or long-distance running events, in hot weather are among the situations that can lead to heatstroke.

  • Sudden exposure to hot weather. People may be more susceptible to heat-related illness when they're exposed to a sudden increase in temperature, such as during an early-summer heat wave or travel to a hotter climate.

    Limit activity for at least several days to allow time to acclimate to the temperature change. However, there may still be an increased risk of heatstroke until a person experiences several weeks of higher temperatures.

  • A lack of air conditioning. Fans may make you feel better, but during sustained hot weather, air conditioning is the most effective way to cool down and lower humidity.

  • Certain medicines. Some medicines affect your body's ability to stay hydrated and respond to heat. Be especially careful in hot weather if you take medicines that narrow your blood vessels (vasoconstrictors), regulate your blood pressure by blocking adrenaline (beta blockers), rid your body of sodium and water (diuretics), or reduce psychiatric symptoms (antidepressants or antipsychotics).

    Stimulants for attention-deficit/hyperactivity disorder (ADHD) and illegal stimulants such as amphetamines and cocaine also make you more vulnerable to heatstroke.

  • Certain health conditions. Certain chronic illnesses, such as heart or lung disease, might increase your risk of heatstroke. So can being overweight, being inactive and having a history of previous heatstroke.

Complications

Heatstroke can result in a number of complications, depending on how long the body temperature is high. Serious complications include:

  • Vital organ damage. Without a quick response to lower the body temperature, heatstroke can cause the brain or other vital organs to swell, possibly resulting in permanent damage.
  • Death. Without prompt and adequate treatment, heatstroke can be fatal.

Prevention

Heatstroke is predictable and preventable. Take these steps to prevent heatstroke during hot weather:

  • Wear loose-fitting, lightweight clothing. Excess clothing or clothing that fits tightly doesn't allow your body to cool properly. Clothes made of linen, silk, cotton or hemp are cooling.
  • Protect against sunburn. Sunburn affects your body's ability to cool itself, so protect yourself outdoors with a wide-brimmed hat and sunglasses. And use a broad-spectrum sunscreen with an SPF of at least 15. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or sweating.
  • Drink plenty of fluids. Stay hydrated to help your body sweat and maintain a normal body temperature.
  • Take extra precautions with certain medicines. Be on the lookout for heat-related problems if you take medicines that can affect your body's ability to stay hydrated and dissipate heat.

  • Never leave anyone in a parked car. This is a common cause of heat-related deaths in children. When a car is parked in the sun, the temperature in the car can rise 20 degrees Fahrenheit (more than 11 degrees Celsius) in 10 minutes.

    It's not safe to leave a person in a parked car in warm or hot weather, even if the windows are cracked or the car is in shade. When your car is parked, keep it locked to prevent a child from getting inside.

  • Take it easy during the hottest parts of the day. If you can't avoid strenuous activity in hot weather, drink fluids and rest frequently in a cool spot. Try to schedule exercise or physical labor for cooler parts of the day, such as early morning or evening.
  • Get acclimated. Limit time spent working or exercising in heat until you're conditioned to it. People who are not used to hot weather are especially susceptible to heat-related illness. It can take several weeks for your body to adjust to hot weather.

Be cautious if you're at increased risk. If you take medicines or have a condition that increases your risk of heat-related problems, avoid the heat and act quickly if you notice symptoms of overheating. If you participate in a strenuous sporting event or activity in hot weather, make sure there are medical services available in case of a heat emergency.

By Mayo Clinic Staff