Heatstroke is a life-threatening condition that occurs when your body temperature reaches 104 F (40 C) or higher. Heatstroke can be brought on by high environmental temperatures, by strenuous physical activity or by other conditions that raise your body temperature.

What is it?

  • Heatstroke is a life-threatening condition that occurs when your body temperature reaches 104 F (40 C) or higher. Heatstroke can be brought on by high environmental temperatures, by strenuous physical activity or by other conditions that raise your body temperature. Whatever the cause, you'll need immediate medical attention to prevent brain damage, organ failure or death.
  • Heatstroke is the escalation of two other heat-related health problems: heat cramps and heat exhaustion. In these conditions, you develop signs and symptoms that are milder than those of heatstroke. You can prevent heatstroke if you receive medical attention or take self-care steps as soon as you notice problems.


Heatstroke symptoms include:

  • High body temperature. A body temperature of 104 F (40 C) or higher is the main sign of heatstroke.
  • A lack of sweating.
In heatstroke brought on by hot weather, your skin will feel hot and dry to the touch. However, in heatstroke brought on by strenuous exercise, your skin usually feels moist.
  • Flushed skin. Your skin may turn red as your body temperature increases.
  • Rapid breathing. Your breathing may become rapid and shallow.
  • Racing heart rate and strong pulse (tachycardia). Your pulse may significantly increase because heat stress places a tremendous burden on your heart to help cool your body.
  • Headache. You may experience a throbbing headache.
  • Neurological symptoms. You may have seizures, lose consciousness, slip into a coma, hallucinate, or have difficulty speaking or understanding what others are saying.
  • Muscle cramps or weakness. Your muscles may feel tender or cramped in the early stages of heatstroke, but may later go rigid or limp.
  • Causes

    Heatstroke is the escalation of two less serious heat-related conditions. If you don't take steps to treat these lesser conditions quickly, your condition may worsen and become heatstroke:

    • Heat cramps. Heat cramps are caused by initial exposure to extreme temperatures or physical exertion. Signs and symptoms of heat cramps usually include profuse sweating, fatigue, thirst and muscle cramps, usually in the stomach, arms or legs. This condition is common in warmer weather or with moderate to heavy physical activity. You can usually treat heat cramps by drinking fluids containing electrolytes (Gatorade or other sports drinks), resting and getting to a cool spot, like a shaded or air-conditioned area.
    • Heat exhaustion. Heat exhaustion occurs when you don't act on the signs and symptoms of heat cramps and your condition worsens. Signs and symptoms of heat exhaustion include a headache, dizziness or lightheadedness, nausea, skin that feels cool and moist, and muscle cramps. Often with heat exhaustion, you can treat the condition yourself by following the same measures used to treat heat cramps, such as drinking cool nonalcoholic beverages, getting into an air-conditioned area or taking a cool shower. If your symptoms persist, seek medical attention immediately.

    The cause of your heatstroke depends on the activities you do that bring on your condition. Heatstroke can occur in these ways:

    • Environmental conditions. In a type of heatstroke called nonexertional heatstroke, your condition is caused by extreme environment temperatures that cause your body temperature to increase. You may be doing some light or moderate activity, but activity is not the primary cause of your heatstroke. This type of heatstroke is typical in warmer, more humid weather.
    • Strenuous activity. In a type of heatstroke called exertional heatstroke, your condition is caused by strenuous activity that increases your body temperature. You can have exertional heatstroke even if you're accustomed to working or exercising in very hot temperatures, though heatstroke is more likely to occur if you're not accustomed to high temperatures.

    In either exertional or nonexertional heatstroke, your condition can be brought on by:

    • Wearing excess clothing that doesn't allow your sweat to evaporate easily
    • Drinking alcohol, which can affect your body's ability to regulate your temperature
    • Dehydration

    Risk factors

    Anyone can have heatstroke, but several factors may place you at greater risk:

    • Young or old age. Your ability to cope with extreme heat depends of the vitality of your central nervous system. In the very young, the central nervous system is not fully developed, and in adults over 65, the central nervous system begins to deteriorate, which makes your body less able to cope with changes in body temperature. Both age groups usually have difficulty remaining hydrated as well, also increasing risk.
    • Genetic response to heat stress. To some degree, the way your body responds to extreme heat is determined by genetics. Researchers believe that your genes may play a vital role in determining how your body will respond in extremely hot conditions.
    • Hot-weather intolerance. If you're not used to high temperatures or high humidity, you may be more susceptible to heat-related illness if you're exposed to a sudden increase in temperature, as might happen with a heat wave that occurs during late spring. Limit your physical activity for at least several days until you've acclimated to the higher temperatures and humidity. However, you may still have an increased risk of heatstroke until you've experienced several weeks of higher temperatures.
    • A lack of air conditioning. Fans may make you feel better, but in sustained hot weather, air conditioning is the most effective way to cool down and lower the humidity.
    • Spending time outdoors. If you have to work outside, or you participate in school or professional sports that require you to practice outdoors in the summer, you have a higher risk of heatstroke.
    • Certain medications. Some medications place you at a greater risk of heatstroke and other heat-related conditions because they affect your body's ability to stay hydrated and respond to heat. Be especially careful in hot weather if you take medications 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). Additionally, stimulants, such as amphetamines and cocaine, increase your body's heat production, making you more vulnerable to heatstroke.


    A possible complication of heatstroke is shock, which is a condition caused by a sudden loss of blood flow. Signs of shock include a very low blood pressure, blue lips and nails, and cool, clammy skin. Shock can damage your organs if it's not treated quickly.

    If you don't act quickly on the other symptoms of heatstroke, you could die or experience damage to your brain or other vital organs. In response to heatstroke, these organs swell, and if you don't cool your body temperature quickly, the damage from this swelling could be permanent.


    It's usually apparent to doctors if you have heatstroke, but they may order laboratory tests to confirm their diagnosis. These tests include:

    • A blood test to check for low blood sodium or potassium and the content of gases in your blood to see if there's been any damage to your central nervous system
    • A urine test to check the color of your urine, because it's usually darker if you have a heat-related condition, and to assess your kidney function, which can be affected by heatstroke
    • Muscle function tests to check for rhabdomyolysis — serious damage to your muscle tissue
    • X-rays and other imaging tests to check for other damage to your internal organs