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.
• Cessation of sweating. This is often one of the first signs that your body temperature is too high. In heatstroke brought on by hot weather, your skin is hot and dry to the touch. However, in heatstroke brought on by strenuous exercise, your skin usually feels moist.
• Hyperventilation. Your breathing may become rapid and shallow.
• Rapid heart rate and pulse (tachycardia). While your blood pressure usually remains normal, your pulse may increase to around 130 beats a minute, well above the normal level for adults (60 to 100 beats a minute). This is because heat stress places a tremendous burden on your heart to help cool your body.
• 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.

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. 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 dark urine. Often with heat exhaustion, you can treat the condition yourself by following the same measures used to treat heat cramps. 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 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 suffer exertional heatstroke even if you're accustomed to working or exercising in very hot 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

Anyone can suffer from 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 older adults, 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.

• 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 careful in hot weather if you take medications that narrow your blood vessels (vasoconstrictors, such as ergotamine), regulate your blood pressure by blocking adrenaline (beta blockers, such as atenolol), rid your body of sodium and water (diuretics, such as hydrochlorothiazide), or reduce psychiatric symptoms like delusions (neuroleptics, such as olanzapine).

If you think you have the beginning of heatstroke, first try to cool yourself and replenish your water and salt levels. If your condition has progressed past heat cramps and heat exhaustion and you feel any of the symptoms of heatstroke, seek immediate medical attention.

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 — damage to your muscle tissue
• X-rays and other imaging tests to check for other damage to your internal organs

The most immediate complication of heatstroke is shock. Shock occurs when your body doesn't get enough blood flow, which 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 suffer 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.

Heatstroke treatment centers on cooling your body to a normal temperature quickly to prevent or reduce damage to your brain and vital organs. To do this, your doctor may:

• Immerse you in cold water. Your doctor may immerse your body in a bath of cold water or ice water to quickly lower your temperature. This method has fallen out of favor with some doctors because it restricts access to your body if additional medical evaluation or treatment needs to be done, such as inserting an intravenous (IV) line or performing chest compressions.
• Use evaporation cooling techniques. Some doctors prefer to use evaporation instead of immersion to lower your body temperature. In this technique, your doctor mists cool water on your skin and fans warm air over your body to evaporate the water on your skin.
• Pack you with ice and cooling blankets. Another method is to wrap you in a special cooling blanket and pack your groin, neck, back and armpits with ice packs to lower your temperature.
• Stop your shivering. If any treatments to lower your body temperature make you shiver, your doctor may give you a muscle relaxant, such as benzodiazepine. Shivering increases your body temperature, making treatment ineffective.

Although heatstroke is serious, you can easily prevent it. In hot weather, remember to:

• Wear loosefitting, lightweight clothing. Wearing excess clothing or clothing that fits tightly won't allow your body to cool properly by allowing your sweat to evaporate.
• Seek a cooler environment. A good way to start cooling off is to get to a cooler environment, like an air-conditioned building or a shady spot.
• Drink plenty of fluids. Staying hydrated will help your body sweat and maintain a normal body temperature.
• Take extra precautions with certain medications. Several medications can affect your body's ability to stay hydrated. These include medications that narrow your blood vessels (vasoconstrictors, such as ergotamine), regulate your blood pressure by blocking adrenaline (beta blockers, such as atenolol), rid your body of sodium and water (diuretics, such as hydrochlorothiazide), or reduce psychiatric symptoms like delusions (neuroleptics, such as olanzapine).
• Avoid being inside a hot car. When parked in the sun, your car can reach a temperature of over 160 F (71 C). Getting into an environment this hot can be dangerous. Never leave children or anyone else in a parked car in hot weather for any period of time.

It's best not to exercise or do any strenuous activity in hot weather, but if you must, follow the same precautions and rest frequently in a cool spot. Taking breaks and replenishing your fluids during that time will help your body regulate your temperature.

If you notice signs of heat emergencies early, you can take action to lower your body temperature and prevent your condition from elevating to heatstroke. In a heat emergency, you can take these steps for yourself and for others:

• Get to a shady or air-conditioned place. Remaining in the heat will worsen your condition.
• Cool off with damp sheets and a fan. Cool the person by covering him or her with damp sheets or by spraying with cool water. Direct air onto the person with a fan.
• Rehydrate and replenish your salt intake. Keep in mind that the symptoms of heat-related illnesses are caused not only when you become dehydrated, but also when you lose salt through sweating. Sports drinks will replenish both water and salt, or you can drink salted water (1 teaspoon of salt for each quart of water). The amount you'll need to drink to rehydrate varies from person to person, so sip slowly and call your doctor if you're concerned.
• Don't drink beverages with alcohol or caffeine to rehydrate. These drinks may interfere with your body's ability to control your temperature.