Heat Exhaustion


Heat exhaustion is a serious heat illness that occurs when an individual's body temperature rises above normal levels. It can quickly progress into a more serious condition known as heatstroke, which can be fatal.


Heat exhaustion is a serious heat-related illness. It is more serious than heat cramps, but less serious than heatstroke which is potentially life threatening. However, heat exhaustion can become heatstroke quickly and with little warning, making it a very serious condition that should be treated immediately.

Outdoor fitness and recreation enthusiasts need to be especially mindful of heat-related illnesses and take steps to prevent them. Hundreds of individuals in the United States each year require serious medical treatment for heat illness. Although heat exhaustion occurs most frequently on extremely hot days, it can occur at any time that warm temperatures are present, especially when combined with physical exertion.

Heat illnesses are a serious public health threat. During heat waves many schools and other government and community buildings with air conditioning are opened to allow at-risk individuals to stay out of the heat to prevent heat illness. Sports matches, marathons, and other outdoor events lead to more cases of heat illness on very warm days, and additional medical and other staff may be necessary to help ensure prompt treatment of affected individuals.


U.S. tennis player Jack Sock receives medical attention due to heat exhaustion during the U.S. Open in Queens, New York, September 2015. Heat exhaustion can quickly progress into heatstroke, an even more serious illness that can be fatal.

U.S. tennis player Jack Sock receives medical attention due to heat exhaustion during the U.S. Open in Queens, New York, September 2015. Heat exhaustion can quickly progress into heatstroke, an even more serious illness that can be fatal.
(Al Bello/Getty Images)

The exact number of cases of heat exhaustion each year in the United States is unknown, because many people do not seek professional medical treatment unless the problem progresses to heatstroke. It is less common in countries that have cool climates. It is most common in countries that have occasional episodes of unusually high temperatures, such as the United States, Japan, and India. Heat exhaustion is especially problematic among athletes, who often practice outside for long periods even during especially hot weather. Young athletes are especially vulnerable because they dehydrate more easily and may not be as experienced in recognizing the first signs of heat illness.

Risk factors

Individuals who play outdoor sports or who engage in outdoor fitness or recreational activities are at increased risk. Drinking alcoholic beverages or taking excessive amounts of caffeine (from drinks or supplements) also increases the risk of heat illness on hot days, as they can decrease hydration and sometimes impair the ability to sweat. Some medications also can increase the risk of heat illness. Some blood pressure and heart medications, allergy medications, diet pills, diuretics (water pills), cold medicines, medicines to prevent seizures, laxatives, and thyroid pills increase risk for heatstroke. Individuals should talk to their doctor or pharmacist to find out if their medications could increase these risks.

Although anyone can get heat illness, seniors, children, and obese individuals are at higher risk for heat exhaustion. Young children who participate in athletics are especially at risk. Children do not always notice when the first signs of heat illness begin and may be less likely to seek a break to cool off or drink more fluids. Children participating in outdoor activities on hot days should be monitored carefully for signs of heat illness.

Causes and symptoms

Heat exhaustion occurs when the body's natural heat dissipation systems can no longer keep up with the heat being created by the body. The body's cooling system is typically very effective. To cool itself, the body produces sweat, which dampens the surface of the skin. When the air moves over the damp skin, a cooling effect occurs, lowering the body's temperature. If the body cannot cool itself through sweating, either because the amount of sweat being produced is insufficient, or the external environment is so hot that the cooling effect is not enough, the body's internal temperature begins to rise. It is this rise that causes heat illness.

Heat exhaustion can manifest itself in a number of ways. Individuals experiencing heat exhaustion may have one or more of the following symptoms:

Heat exhaustion can occur suddenly after exposure to excessive heat, especially after exercise or rigorous outdoor activities such as jogging, soccer, and tennis. It can also occur more slowly, beginning to manifest itself after one or more days of exposure to excessive heat. This is a particularly common onset pattern in the elderly.


Diagnosis of heat exhaustion is generally made by observing the patient's symptoms and obtaining a history of the patient's recent heat exposure and physical activity. The medical team will take the patient's pulse and temperature to help determine how far the heat illness has progressed. If the individual's core temperature is above 104°F (40°C), then the heat exhaustion has likely progressed to heatstroke, a serious life-threatening emergency.


The main goal of treatment for heat exhaustion is to bring body temperature down to a normal level as quickly as possible and to ensure that it does not progress to heatstroke. An individual showing signs of heat exhaustion should immediately stop any activity and be treated right away. Delaying treatment of heat-related illness can lead to serious long-term consequences or even be fatal.

Ions in the body that participate in metabolic reactions. The major human electrolytes are sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl-), phosphate (HPO42-), bicarbonate (HCO3-), and sulfate (SO42-)Careful and regular monitoring of electrolytes and intravenous replacement of fluid and electrolytes are part of the acute care in many illnesses.
Heat cramps—
The least serious of the heat-related illnesses, which can quickly develop into heat exhaustion.
The most serious of the heat-related illness, usually a body temperature over 104°F; can be life-threatening.
Intravenous (IV)—
The process of giving a liquid through a vein.

An individual showing signs of heat exhaustion should be moved to a cool spot out of direct sunlight such as an air-conditioned building or shaded area. Any excessive layers of clothing should be removed. Misting the individual with water and using a fan can help to mimic the effects of sweat and begin to reduce body temperature.

An individual experiencing a heat illness is not properly hydrated. This often means that the individual's electrolytes are imbalanced as well. The individual experiencing heat exhaustion should be given liquids that do not contain caffeine, excessive amounts of sugar (high sugar content can slow the rate of fluid absorption), or alcohol. Cool fluids are best because they both immediately help bring down the individual's body temperature and improve hydration. Improving hydration can help restore the ability to sweat, which in turn will help reduce the person's core temperature. Sports drinks such as Gatorade have a rapid absorption rate and contain nutrients and minerals that can help restore the balance of electrolytes that the body needs.


If treatment does not seem to be effective, emergency medical treatment should be sought immediately. Fluids can be provided intravenously to improve hydration and sweating, special cooling tables can be used to quickly reduce body temperature, and medications can be used to help reduce shivering.


The prognosis for heat exhaustion is generally quite good. With treatment, symptoms should generally begin to improve within an hour. Untreated heat exhaustion can quickly become heatstroke. Heatstroke is a serious medical emergency that requires immediate emergency medical care. Heatstroke is fatal in about 10% of cases in which prompt medical attention is received and in as much as 80% of cases in which treatment is significantly delayed.


Avoiding rigorous exercise on very hot days is the best way to prevent heat exhaustion. Choosing to exercise in an air-conditioned gym instead of jogging outside when it is very hot can help ensure that heat illness does not occur. When playing outdoor sports or engaging in other outdoor activities, it is important to rest frequently in cool areas (such as the shade or an air conditioned building) and to drink plenty of noncaffeinated, non-alcoholic beverages. If hiking, running, or bicycling long distances it is important to bring along enough water for the entire workout, in case water fountains or other facilities are not readily available. Wearing loose clothing on hot days can also help, allowing the body to breath and airflow to cool the skin.

See also Hydration .



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National Athletic Trainers' Association, 1620 Valwood Pkwy., Ste. 115, Carrollton, TX, (214) 637-6282, # http://www.nata.org/ #.

Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.