Heat Illness


What is heat illness?

Heat illness includes heat stroke, heat exhaustion, heat cramps, and heat rash. It often occurs when a person is exercising, working, or engaging in an activity when temperatures and humidity are high.

What are the types of heat illness?

Heat rash and heat cramps are mild types of heat illness.

  • Heat rash is a mild skin irritation caused by heavy sweating.
  • Heat cramps usually develop in muscles being used during the activity. Cramps are caused by the loss of body salts and fluid through heavy sweating and high effort. When a muscle has a low salt level, it cramps.

Heat exhaustion and heat stroke are serious types of heat illness.

  • Heat exhaustion is the body’s general reaction to losing salt and fluid through heavy sweating.
  • Heat stroke usually occurs in very high heat, high humidity conditions. However, heat stroke can also occur in mild to moderately hot temperature if the humidity is high (in other words, if the heat index – the “feels like” temperature – is high). Sweat cannot evaporate as quickly as usual, so the body cannot release heat to cool itself. Sweating stops and the body temperature goes up quickly. Body temperature can rise to dangerous levels – 106°F or more in just 10 to 15 minutes.

Who gets heat illness?

Individuals who exercise or work under hot, humid conditions – inside or out – are at highest risk for heat illness. Exercising or working in the sun on a hot, humid day increases the risk of heat illness.

Other factors that increase the risk for heat illness include:

  • Dehydration (not having enough fluids in the body).
  • Obesity.
  • Use of certain prescription medicines like tranquillizers, water pills, Parkinson’s disease medications, and drugs used to treat mental illness.
  • Illegal drug use.
  • Poor physical fitness or lack of experience working in heat, outdoors, or doing heavy work.
  • Alcohol use.
  • Illness/fever.
  • Clothing that is tight, dark, or heavy.
  • Wearing heavy equipment and clothing (sports padding and helmets; police/fire, personal, industrial protective equipment and clothing).
  • Medical conditions like diabetes, kidney and heart problems including high blood pressure, pregnancy.
  • Age four and younger and 65 and older.
  • Prior history of heat-related illness.

Some of the industries with a high risk for heat illness include construction, transportation and utilities, farming, maintenance, landscaping, and support activities for oil and gas operations. Athletes who compete outside also have an increased risk.

Symptoms and Causes

What causes heat illness?

Normal body temperature is balanced through heat production and heat loss. A heat-related illness occurs when the body is not able to regulate, or control, its temperature. Heavy sweating disturbs the body’s normal salt-water balance, which causes the symptoms of heat illness.

Most cases of heat illness occur when a person is exercising, working, or engaging in an activity when the temperature and humidity are both high. Under these conditions, sweat cannot evaporate from the skin (the body’s natural cooling system), and the body’s temperature begins to rise. If left untreated, a heat illness can lead to serious complications, even death. If detected and treated early, however, most serious problems can be avoided.

What are the symptoms of the different types of heat illness?

Heat stroke

Heat stroke is a medical emergency. Call 911 immediately if a person has any of these symptoms:

  • Temperature of 103°F or higher.
  • Throbbing headache.
  • Nausea.
  • Muscle twitching.
  • Red, hot, dry skin.
  • Confusion, altered mental state, slurred speech.
  • Dizziness or fainting.
  • Rapid pulse.
  • Seizures.
  • Lack of sweating.
  • Hallucinations.
  • Loss of consciousness.

Heat exhaustion

  • Heavy sweating.
  • Muscle cramps.
  • Cool, moist skin.
  • Headache.
  • Nausea.
  • Dizziness.
  • Fainting.
  • Weakness.
  • Irritability
  • Pale skin color.
  • Weak and quick pulse.
  • Quick and shallow breathing.
  • Thirst.

Heat cramps

  • Muscle pain or spasm—usually in the legs, arms, or abdomen.

Heat rash

  • Small red bumps or small blisters on the skin in areas that stay wet from sweat—usually on the upper chest, neck, inside of the elbow.

Can heat illness cause serious problems?

Heat stroke is the most serious form of heat illness. Heat stroke can cause blood disorders and damage to the heart, liver, kidneys, muscles, and nervous system. Heat stroke can lead to death if the person does not receive emergency medical treatment.

When a person with heat exhaustion does not receive treatment, the illness can worsen and become heat stroke. An individual with heat exhaustion is at higher risk for accidents because heat exhaustion often causes tiredness, confusion, and decreased alertness.

Diagnosis and Tests

When is it necessary to seek medical treatment for a heat illness?

  • Heat stroke: Call 911 if any heat stroke symptoms are present.
  • Heat exhaustion and heat cramps: If symptoms get worse or do not improve in an hour, call 911.

Management and Treatment

What is the treatment for heat illness?

Heat stroke

Call 911 immediately.

The best treatment for heat stroke is immediate cooling in an ice bath. It takes ice and water to efficiently cool the body. Do not delay. If heat stroke occurs at a location where an ice bath is not possible, move the individual to a cool area if indoors or a cool, shady area if outdoors. Loosen or remove the person’s clothing. Have the person lie down and slightly elevate the feet. Cool the person as quickly as possible. Wet the person’s skin with cool water, place cool cloths or ice all over the body, spray the person with a garden hose or soak the person’s clothes with cold water. Check the person’s temperature and continue these efforts until his/her temperature is 101°F or lower. Do NOT give the person fluids to drink. Continue your efforts until medical help arrives.

Heat exhaustion

While waiting for medical help, move the individual to a cool area if indoors or to a cool, shady area if outdoors. Give the person cool water to drink in small sips. Cool head, face, and neck with cold ice packs, cold cloths or cold water. When symptoms improve, take the individual to a clinic or emergency room to be seen by a nurse or doctor.

Heat cramps

Heat cramps usually can be treated by rest and fluids. The person should stop the activity and rest in a cool place. Have him/her drink apple or grape juice or a sports drink in small sips every 15 to 20 minutes. He or she should rest for several hours before going back to work or exercise.

Heat rash

Talcum powder will soothe heat rash. Do not apply lotions or ointments. To prevent heat rash from coming back, the skin must be kept dry.


How can heat illness be prevented?

  • Drink water every 15 minutes when working or exercising in a hot environment, even if you are not thirsty. If you need to be out in extreme heat (heat index over 103°F), drink a total of 2 to 4 cups (16 to 32 ounces) of water each hour.
  • Take periodic rest breaks in the shade, cool area, or air-conditioned space.
  • When working or exercising outside in hot humid weather, wear a hat and loose, lightweight, light-colored clothing.
  • Do not drink alcohol or caffeine-containing beverages.
  • Avoid going outdoors for activities or exercise if possible when the temperature and humidity are high.

Outlook / Prognosis

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

People with heat rash, heat cramps, or heat exhaustion usually recover quickly after treatment. How long it takes a person to recover from heat stroke depends on the person’s age, physical condition, and how quickly he or she receives medical care. A person who has had heat exhaustion or heat stroke may be more sensitive to hot conditions for up to a week after the event. Check with your doctor before returning to work or activities.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy