Heat Illness

If your body is overheating, and you have a high temperature, bumps on your skin, muscle spasms, headache, dizziness, nausea or a number of other symptoms, you may have one of the most common heat-related illnesses: heat rash, heat cramps, heat exhaustion or heat stroke. Heat illnesses range from mild to severe, and heat stroke can be deadly.


What are heat illnesses?

A heat illness is one caused by high temperatures and humidity. You may get an illness while exercising or working in high heat and humidity. The four most common heat illnesses include:

  • Heat rash (also called prickly heat or miliaria), which is a stinging skin irritation that turns your skin red.
  • Heat cramps, which are painful spasms in your muscles.
  • Heat exhaustion, which is caused by too few fluids and long hours in high temperatures, causes heavy sweating, a fast and weak pulse and rapid breathing.
  • Heat stroke, which is a life-threatening illness, happens when your temperatures rises above 106 degrees Fahrenheit (41 degrees Celsius) quickly – within minutes.

Your body sweats to keep itself cool. If temperatures and humidity are too high, sweating isn’t effective enough.


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How does the body stay cool?

The process that helps your body keep a healthy core temperature is called thermoregulation. Thermoregulation is controlled by a region of your brain called the hypothalamus. It activates receptors in your skin and other organs that cause you to lose heat and keep a normal core temperature. When your body gets really hot, it relies on sweat evaporation to dissipate heat (make the heat go away). If the heat entering your body is more than the rate of heat leaving your body, your core temperature will rise and you’ll be at risk for a heat-related illness.

What are the types of heat illnesses?

Heat illnesses are categorized as either mild or severe. The mild types include:

  • Heat rash.
  • Heat cramps.

The severe types include:

  • Heat exhaustion.
  • Heat stroke.

Who gets heat illnesses?

If you work outside, or inside in a hot and humid environment, you’re more likely to endure a heat illness. Examples of people who might be in such an environment include:

  • Construction workers.
  • Athletes.
  • Military personnel.
  • Firefighters.
  • Landscapers.
  • Farmers.
  • Maintenance workers.
  • Utility workers.

Additional factors that increase your risk of getting a heat illness include:

  • Dehydration. If you’re dehydrated, meaning you don’t have enough fluids in your body, you’re more at risk of a heat illness.
  • Obesity and/or poor physical fitness.
  • Certain prescription medications. These include tranquilizers, water pills, antihistamines, beta blockers, laxatives and drugs used to treat mental illnesses or Parkinson’s disease.
  • Using illegal drugs or alcohol.
  • Lack of experience working in heat, working outdoors or doing heavy work. You may need to take breaks and spend some time in the shade.
  • Illness, specifically medical conditions such as diabetes, kidney problems and heart problems. Also pregnancy, and symptoms like high blood pressure and fever.
  • Heavy, dark or light clothing. If you must wear heavy equipment and clothing like sports padding and helmets, police and fire uniforms and industrial protective equipment, you’re in danger of developing a heat illness.
  • Age. If your child is four years old or younger, or you’re 65 or older, you’re at a higher risk. Infants and young children commonly get heat rash.
  • Gender. Males are more likely to get a heat illness than females.
  • Prior history of heat-related illnesses.

How common are heat illnesses?

Statistics about student athletes state that there are around 9,000 cases of heat-related illnesses per year. Most occur during football season. Heat illnesses are the third leading cause of death in high school athletes.

In the U.S. Armed Forces in 2017, there were 2,163 cases.

Emergency departments saw 326,497 cases of heat-related illnesses. Around 12% of those patients were admitted into a hospital and 0.07% of that total died.

What’s the difference between a heat illness and a fever?

A fever is a symptom of an illness, not an illness itself. It’s a higher-than-normal body temperature, but it’s caused by an infection instead of external high heat and humidity.


Do heat illnesses cause sunburn, burns or permanent scars?

No. A heat illness is not like a sunburn, which injures your skin. It’s also not like being in a house fire that may leave scars. Heat rashes don’t permanently damage your skin.

Can heat rash cause skin cancer?

No. Cancer is not a complication of any heat illness.

What should I do to keep my child from getting a heat illness?

Keep a careful eye on infants and young children because they’re at high-risk for a heat-related illness. Consider the following tips:

  • Don’t leave a child in the car, even if a window is cracked.
  • Make sure they drink enough water.
  • Reapply their sunscreen frequently.

What should I do to keep my elderly friend or family member from getting a heat illness?

People age 65 and older are at a higher risk of heat illness, even if they’re not exercising. Reasons include:

  • Serious medical conditions such as heart disease.
  • Some medications, especially those for insomnia, poor circulation or depression.
  • Lack of air conditioning in their homes.

Caretakers should familiarize themselves with the symptoms of heat illnesses so that they can recognize them quickly. Check in twice a day during a heat wave.

Make sure they stay hydrated. The signs of dehydration include dry skin and decreased urination.

Symptoms and Causes

What causes heat illnesses?

As the name of the illness suggests, it’s caused by heat – excessive heat that increases your body’s core temperature. That heat could come from exercising, from being inside a hot space or from outside weather. High humidity – greater than 60% – makes sweat evaporation hard. A heat illness happens when your body is s unable to dissipate heat effectively, the balance of salt and water in your body becomes unbalanced and your temperature rises. Sweating fails to keep you cool.

The four heat illnesses are on a continuum with heat rash being the mildest and heat stroke the deadliest. Specific causes of the four illnesses include:

  • Heat rash happens when your excessive sweat gets trapped under your skin, blocking your sweat glands.
  • Heat cramps occur when you’re sweating so much, losing salt (electrolytes) and fluids, that your muscles cramp. It usually happens when you’re exercising in the heat.
  • Heat exhaustion. This illness may happen after a longer period of time in high temperatures where you don’t receive enough fluids.
  • Heat stroke is caused by a quick increase in core temperature as a result of high heat and humidity.

Some symptoms are similar between the four heat illnesses, but each also has distinctive symptoms that separate it from the other three. Pay attention to the unique symptoms so that you can tell the difference between the illnesses.

Symptoms of heat rash include:

  • Red skin.
  • Itchy skin.
  • Pain that is tingling or “prickly.”
  • Small bumps or blisters where your skin touches more of your skin, especially your neck, groin, underneath your breasts, armpits or in the creases of your elbows.
  • Small bumps or blisters on areas that stay wet when you sweat. These locations include your neck and the inside of your elbow, but also your upper chest.
  • Infection.

Symptoms of heat cramps include:

  • Muscle pain in the legs, arms or abdomen.
  • Muscle spasms in the legs, arms or abdomen.
  • Body temperature remains normal.
  • Cool, moist skin.

Symptoms of heat exhaustion include:

  • Quick, shallow breathing.
  • Heavy sweating and thirst.
  • Muscle cramps.
  • Headache and irritability.
  • Elevated body temperature and heart rate.
  • Weak, quick pulse.
  • Moist, cool skin. Pale skin color.
  • Nausea, vomiting and diarrhea.
  • Decrease in urination.
  • Dizziness, weakness, lack of coordination and fainting.

Note that heat exhaustion doesn’t affect your mental status. You should be checked by a healthcare provider.

Symptoms of heat stroke include:

  • A quick, strong pulse.
  • Dizziness, fainting, loss of consciousness.
  • Slurred speech, confusion, agitation, hallucinations, altered mental state.
  • Dry, red, hot skin.
  • Nausea.
  • Temperature of 105 degrees Fahrenheit or higher.
  • Muscle twitching.
  • Seizures.
  • Hyperventilation.
  • No sweating despite the heat, humidity.

Heat stroke is a medical emergency. It can lead to organ failure and death. Call 911 or go to the emergency room immediately if you have symptoms.

Diagnosis and Tests

How are heat illnesses diagnosed? What tests are done?

Just like how there are common symptoms between the four heat illnesses, there are also common methods of diagnosis. These methods include:

  • Heat rash. Diagnosing heat rash is fairly straightforward because your healthcare provider can evaluate it by examining your skin. If your heat rash is mild, you might not even need to see your healthcare provider. However, see one if the rash doesn’t go away after three to four days, or if it seems to be getting worse.
  • Heat cramps. You might not need to see a healthcare provider for your heat cramps, but if you do, they’ll first take your temperature using a thermometer. This tells them your core temperature. They’ll ask you to describe your pain and how often you feel it. Tell your healthcare provider about all of your symptoms.
  • Heat exhaustion. Just like with heat cramps, your healthcare provider will start by taking your temperature. You’ll be interviewed about what you were doing before you came to the emergency room. Were you outside working in the sun? Were you inside in a hot, enclosed space? Your provider will also want to know about your symptoms. For example, how tired (fatigued) are you and have you passed out (fainted) from the exhaustion?
  • Heat stroke. Heat stroke can be deadly. When you go to the emergency room to see a healthcare provider – and you shouldn’t hesitate to go to the emergency room – they’ll take your temperature, test for organ dysfunction, take a complete blood count, examine your electrolytes and calcium, check your urine and take other tests if needed. If it’s not obviously heat stroke, your provider may test you for an infection, drugs, stroke, thyroid problems and other issues. If you’re diagnosed with heat stroke, you may be admitted into the hospital.

What questions might my healthcare provider ask to diagnose a heat illness?

  • What are your symptoms?
  • When did your symptoms start?
  • How long have you had the symptoms?
  • What were you doing before you in came to get checked out?
  • Have you been sweating?
  • Did you lose consciousness?
  • Are you tired?
  • Did you have a seizure?

Management and Treatment

How are heat illnesses treated?

You may be able to treat mild heat illnesses yourself (heat rash and heat cramps) at home, but if the symptoms don’t go away or you have the symptoms of heat exhaustion or heat stroke, you should go to the emergency room. The treatments for the four heat illnesses include at-home remedies, outpatient treatment and inpatient treatment:

Heat rash:

  • Go somewhere cool – inside and air-conditioned, if possible.
  • Gently dry off your skin.
  • Put cold compresses on your skin.
  • Don’t use any products that could block your pores. That includes baby powder, creams and ointments.
  • See your healthcare provider if the symptoms don’t improve.

Heat cramps:

  • Drink water.
  • Rest.

Heat exhaustion:

  • Get to a cool, shaded area or go indoors.
  • Drink cold water with small sips.
  • Put cold cloths on your skin.
  • Spray yourself with mist and stand near a fan.
  • Go to the emergency department or call 911.

Heat stroke:

  • Get out of the hot area.
  • Immediately go to the emergency department or call 911.
  • Get treatment within 30 minutes of symptoms.
  • Start to cool down by spraying yourself with water or applying cool compresses.
  • Loosen or remove your clothing.
  • Elevate your feet.
  • Don’t drink any fluids.


How can I prevent a heat illness? What can I do to reduce my risk of heat illnesses?

Heat illnesses are very preventable. Use the following simple steps to keep yourself from getting overheated:

  • Drink water every 15 minutes when working or exercising in a hot environment, even if you’re not thirsty. If you need to be out in extreme heat (heat index over 103°F), drink a total of two to four glasses (16 to 32 ounces) of water each hour.
  • Take periodic rest breaks in the shade, a cool area or air-conditioned space.
  • When working or exercising outside in hot, humid weather, wear a hat and loose, lightweight, light-colored cotton clothing.
  • Do not drink alcohol or beverages that contain caffeine.
  • Avoid going outdoors for activities or exercise when the temperature and humidity are high.
  • Wear sunscreen. A sunburn reduces your body’s ability to cool down. It can also dehydrate you.
  • Wear a wide-brimmed hat and sunglasses outside.
  • Avoid eating a hot, heavy meal.
  • Pace yourself. Rest often.
  • Monitor your urine output. If you urinate too much you could have a heat illness.

Remember that your body needs electrolytes, not just water. You can get electrolytes from common sports drinks, or powders you can add to your water. Choose an electrolyte drink or solution that’s low in sugar.

Outlook / Prognosis

What’s the prognosis (outlook) for people who have a heat illness?

Patients adequately cooled within 30 minutes will likely have an excellent outlook.

If you have heat rash, heat cramps or heat exhaustion, you should recover quickly after treatment. How long it takes you to recover depends on your age, general physical condition and how quickly you receive medical care. If you have heat stroke it may take you a few days to recover and you might be more sensitive to hot conditions for a week.

You may want to check with your healthcare provider for permission to return to work or activities.

Are there long-term complications of heat illnesses?

After you’re treated for a heat illness, you may be sensitive to heat for up to a week.

When you have heat stroke you’re at a higher risk for the following diseases:

Your healthcare provider may keep you in the hospital for observation and ongoing treatment.

Living With

Can I live a normal life with a heat illness?

Fortunately, heat illnesses are temporary conditions. They won’t affect your quality of life for long, unless there are complications from heat stroke.

How do I take care of myself?

First, do your best to prevent the heat illness. If you do get symptoms, try to cool down within 30 minutes. If you’re within the 30 minute window, your outlook is the best.

Don’t rely on your coach, caretaker or supervisor at work to take care of you. Know the symptoms yourself and how to treat them.

When should I go to the emergency department?

Go to the emergency department if you have symptoms of heat exhaustion or heat stroke. Try to get there within 30 minutes of noticing the symptoms.

What questions should I ask my healthcare provider about heat illnesses?

  • Should I not exercise?
  • What do I need to do differently to prevent heat illnesses in the future?
  • Can I continue to do the activities that caused the illness?
  • When can I return to work/school/normal activities?

A note from Cleveland Clinic

Heat illnesses should not be taken lightly. You have to keep an eye on yourself when your body overheats. A heat rash may be troublesome, but heat stroke can be deadly. Familiarize yourself with the symptoms of heat illnesses to keep yourself and your friends and family safe in hot and humid weather.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 04/01/2021.

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