Heatstroke: Symptoms, Diagnosis, and Treatment

Medically Reviewed by Poonam Sachdev on January 26, 2025
6 min read

Heatstroke happens when your body temperature rises very high, usually because of being in a hot environment. It can damage your brain and other internal organs and be fatal. 

It often happens as milder heat-related illnesses, such as heat cramps, heat syncope (fainting), and heat exhaustion, get worse. But it can happen even without any previous signs of heat injury. Common symptoms include nausea, seizures, confusion, disorientation, and sometimes loss of consciousness or coma .

Also known as sunstroke, heatstroke is the most serious form of heat injury and is considered a medical emergency. If you think you or someone else has heatstroke, call 911 immediately.

Difference between heat exhaustion and heatstroke

Heat exhaustion and heatstroke are both heat-related illnesses, but they differ in severity. Heat exhaustion is a milder condition, with symptoms such as sweating a lot, dizziness, headache, nausea, and weakness. With proper treatment, heat exhaustion isn't an emergency. However, without proper treatment, it can lead to heatstroke.

The hallmark symptom of heatstroke is a core body temperature above 104 F. 

Other symptoms may include:

  • Throbbing headache
  • Dizziness and lightheadedness
  • Lack of sweating despite the heat or excessive sweating
  • Skin flushing
  • Muscle weakness or cramps
  • Nausea and vomiting
  • Rapid heartbeat
  • Rapid, shallow breathing
  • Behavioral changes such as confusion, disorientation, or staggering

What is exertional heatstroke?

This type of heatstroke is caused by doing intense physical activity in hot weather. It's most common in people who aren't used to such a climate.

If you think that someone has heatstroke, immediately call 911 or take the person to a hospital. Any delay in seeking medical help can be fatal.

While waiting for the paramedics to arrive, begin first aid. Move the person to an air-conditioned environment or at least a cool, shady area, and remove any unnecessary clothing.

If possible, take the person's core body temperature and start first aid to cool it to 101-102 F. (If no thermometers are available, don't hesitate to begin first aid.)

Try these cooling strategies:

  • Fan air over the person while wetting their skin with water from a sponge or garden hose.
  • Apply ice packs to their armpits, groin, neck, and back.
  • Put the person in a shower or tub of cool water.
  • If the person loses consciousness and stops breathing, start cardiopulmonary resuscitation (CPR).

 

Heatstroke is most likely to affect older people who live in apartments or homes that don't have air conditioning or good airflow. Other high-risk groups include people of any age who don't drink enough water, have chronic diseases, or drink too much alcohol.

Heatstroke is strongly related to the heat index, which is a measurement of how hot you feel when relative humidity and air temperature are combined. A relative humidity of 60% or more slows sweat evaporation, making it harder for your body to cool itself.

The risk of heat-related illness dramatically increases when the heat index climbs to 90 degrees or more. So it's important, especially during heat waves, to pay attention to the reported heat index. Also, remember that exposure to full sunshine can increase the reported heat index by 15 degrees.

If you live in an urban area, you may be at a higher risk for heatstroke during a prolonged heat wave, particularly if there is stagnant air and poor air quality. In what is known as the "heat island effect," asphalt and concrete store heat during the day and only gradually release it at night, resulting in higher nighttime temperatures.

Other risk factors associated with heat-related illness include:

Age. Infants and children up to age 4 and adults over age 65 are particularly vulnerable because they adjust to heat more slowly than other people.

Health conditions. These include heart, lung, or kidney disease, obesity or underweight, high blood pressure, diabetes, mental illness, sickle cell trait, alcoholism, sunburn, and any conditions that cause fever.

Medications. These include antihistamines, diet pills, diuretics, sedatives, tranquilizers, stimulants, seizure medications (anticonvulsants), heart and blood pressure medications such as beta-blockers and vasoconstrictors, and medications for psychiatric illnesses such as antidepressants and antipsychotics. Illegal drugs such as cocaine and methamphetamine also are associated with an increased risk of heatstroke.

Check with your doctor to see if your health conditions and medications are likely to affect your ability to deal with extreme heat and humidity.

When the heat index is high, it's best to stay in an air-conditioned environment. If you must go outdoors, you can prevent heatstroke by taking these steps:

Dress for hot weather. Wear lightweight, light-colored, loose-fitting clothing, and a wide-brimmed hat.

Use sunscreen with an SPF of 30 or more. Sunburn can make it harder for your body to cool itself.

Drink extra fluids. To prevent dehydration, it's generally recommended to drink at least eight glasses of water, fruit juice, or vegetable juice per day. Because heat-related illness also can result from salt depletion, it may be advisable to substitute an electrolyte-rich sports drink for water during extreme heat and humidity.

Take additional precautions when exercising or working outdoors. The general recommendation is to drink 24 ounces of fluid two hours before exercise, and consider adding another 8 ounces of water or sports drink right before exercise. During exercise, you should consume another 8 ounces of water every 20 minutes, even if you don't feel thirsty.

Reschedule or cancel outdoor activity. If possible, shift your time outdoors to the coolest times of the day, either early morning or after sunset.

Other strategies for preventing heatstroke include:

Monitor the color of your urine. Darker urine is a sign of dehydration. Be sure to drink enough fluids to maintain very light-colored urine.

Measure your weight before and after physical activity. Monitoring lost water weight can help you determine how much fluid you need to drink.

Avoid fluids containing caffeine or alcohol .Both substances can make you lose more fluids and worsen heat-related illness. Also, do not take salt tablets unless your doctor has told you to do so. The easiest and safest way to replace salt and other electrolytes during heat waves is to drink sports beverages or fruit juice.

Check with your doctor before increasing liquid intake if you have epilepsy or heart, kidney, or liver disease; are on fluid-restricted diets; or have a problem with fluid retention.

If you live in an apartment or house without fans or air conditioning, try to spend at least 2 hours each day -- preferably during the hottest part of the day -- in an air-conditioned environment. At home, draw your curtains, shades, or blinds during the hottest part of the day, and open windows at night on two sides of your building to create cross-ventilation.

Recovering from heatstroke can take about a week or longer. It depends on your age, the severity of your heatstroke, and any medical conditions you may have. Try to avoid hot weather and heavy exercise until your doctor tells you that it's safe to resume your normal activities.

Heatstroke is a medical emergency that requires immediate treatment. Call 911 if you or someone you're with is showing signs of the illness, including headache, muscle weakness, dizziness, confusion, nausea and vomiting, and rapid breathing and heart rate. Heatstroke can be prevented by avoiding outdoor activity in hot weather, drinking plenty of fluids, staying in the shade, wearing sunscreen, and wearing light, breathable clothing.

Can heatstroke be treated at home?

Heatstroke is a medical emergency that cannot be treated at home. Call 911 if you think you or someone else has heatstroke. 

What food items can prevent heatstroke in summer?

Staying hydrated can help prevent heatstroke. Drinking plenty of water is key, but you can also eat water-rich foods to get the hydration and minerals your body needs. Some good foods include watermelon, cucumber, celery, and oranges.