Hundreds of children die each year of heatstroke after being left in parked cars. People who are poor and experience power outages or who lack cooling equipment are more vulnerable to heat disorders. In 2017, ten undocumented immigrants died from the heat while being smuggled inside a closed metal trailer, and at least 25 others had ill effects from the heat. The Environmental Protection Agency has reported a rise in average temperature and extreme heat (much hotter temperatures than average) since the 1960s in the United States and around the world, likely because of climate change.
Heat disorders are harmful to people of all ages, but their severity typically increases as people age. Heat cramps in a 16-year-old may be heat exhaustion in a 45-year-old and heat stroke in a 65-year-old.
Regardless of extreme weather conditions, the healthy human body keeps a steady temperature of approximately 98.6°F (37°C). The body's temperature-regulating mechanisms rely on thermal regulating centers in the brain. Through these complex centers, the body tries to adapt to high temperatures by adjusting the amount of salt in perspiration. Salt helps the cells in body tissues retain water. In hot weather, a healthy body will lose enough water to cool the body while creating the lowest level of chemical imbalance. The water loss during hot weather or vigorous activity is from perspiration. As perspiration evaporates from the skin, the body is cooled. However, if the body loses too much salt and fluids, symptoms of dehydration can occur.
Very young children, very old adults, and individuals who are obese or have cardiovascular problems are at increased risk of experiencing a heat disorder. Alcohol and diseases that impair the ability to sweat are associated with a higher risk of heat-related illness.
Individuals taking certain medications are more likely to be affected because the medications can interfere with the body's normal cooling mechanisms. Individuals taking certain blood pressure and heart medications, allergy medications, diet pills, diuretics (water pills), cold medicines, drugs to prevent seizures, laxatives, and thyroid pills are at increased risk for hyperthermia.
Heat cramps are the least severe of the heat-related illnesses. This heat disorder is often the first signal that the body is having difficulty coping with increased temperature. Individuals exposed to excessive heat should think of heat cramps as a warning sign to a potential heat-related emergency.
Heat exhaustion is a more serious and complex condition than heat cramps. Heat exhaustion can result from prolonged exposure to hot temperatures, restricted fluid intake, or failure of temperature regulation mechanisms of the body. It often affects athletes, firefighters, construction workers, factory workers, and anyone who wears heavy clothing in hot, humid weather.
Heat exhaustion can develop rapidly into heatstroke. Heatstroke can be life threatening. Because of its seriousness and the high potential for causing death, anyone noticing early symptoms of heatstroke should seek immediate medical attention. The mortality rate for untreated heatstroke is about 80%. Heatstroke, like heat exhaustion, is the result of prolonged exposure to hot temperatures, restricted fluid intake, and/or failure of temperature regulation mechanisms of the body. However, the severity of impact on the body is much greater with heatstroke than with heat exhaustion.
Heat cramps are painful muscle spasms caused by the excessive loss of electrolytes (salts) due to heavy perspiration. The muscle tissue becomes less flexible, causing pain, difficult movement, and involuntary tightness. Heavy exertion in extreme heat, restricted fluid intake, or failure of temperature regulation mechanisms of the body can lead to heat cramps. This disorder occurs more often in the legs and abdomen than in other areas of the body. Individuals at higher risk are those working in extreme heat, elderly people, young children, people with health problems, and those who are unable to naturally and properly cool their bodies. Individuals with poor circulation and who take diuretics can be at risk when conditions are hot and humid. Disabled individuals who are unable to access water on their own are also at higher risk.
Heat exhaustion is caused by exposure to high heat and humidity for many hours, resulting in excessive loss of fluids and electrolytes through heavy perspiration. The skin may appear cool, moist, and pale. The individual might complain of headache and nausea with a feeling of overall weakness and exhaustion. Dizziness, faintness, and mental confusion often are present, as is a rapid and weak pulse. Breathing becomes fast and shallow. Fluid loss reduces blood volume and lowers blood pressure. Dark yellow or orange urine often is a result of inadequate fluid intake, along with associated intense thirst. Insufficient water and salt intake or a deficiency in the production of sweat place an individual at high risk for heat exhaustion.
Heatstroke is caused by overexposure to extreme heat, resulting in a breakdown in the body's heat regulating mechanisms. The body's temperature reaches a dangerous level, as high as 106°F (41.1°C). An individual with heat stroke has a body temperature higher than 104°F (40°C). Other symptoms include mental confusion with possible combativeness and bizarre behavior, staggering, and faintness.
With heatstroke, a person's pulse becomes strong and rapid (160–180 beats per minute) with the skin taking on a dry and flushed appearance. There is often very little perspiration. The individual can quickly lose consciousness or have convulsions. Before heatstroke, an individual experiences heat exhaustion and the associated symptoms. When the body can no longer maintain a normal temperature, heat exhaustion becomes heatstroke. Heatstroke is a life-threatening medical emergency that requires immediate initiation of life-saving measures.
The diagnosis of heat cramps usually involves observation of symptoms such as muscle cramping and thirst. Diagnosis of heat exhaustion or heatstroke, however, may require a physician to review the medical history, document symptoms, and obtain a blood pressure and temperature reading. The physician also might take blood and urine samples for further laboratory testing. A test to measure the body's electrolytes also can give valuable information about chemical imbalances caused by the heat-related illness.
The care of heat cramps includes placing the individual at rest in a cool environment, while giving cool water with one teaspoon of salt per quart of water or giving a commercial sports drink. Typically, rest and liquids are the only treatment needed for a person to recover. Mild stretching and massaging of muscles follows once the condition improves. The individual should not take salt tablets because doing so can actually worsen the condition. When the cramps stop, the person usually can start activity again if there are no other signs of illness. The individual needs to continue drinking fluids and should be watched carefully for further signs of heat-related illnesses.
An individual who shows signs of heat exhaustion should stop all physical activity and immediately be moved to a cool place out of the sun and preferably to a cool, air-conditioned location. It is important to lie down with feet slightly elevated, remove or loosen clothing, and drink cold (but not iced), slightly salty water or a commercial sports drink. Rest and replacement of fluids and salt usually is all the treatment needed, and hospitalization is rarely required. Following rehydration, the person usually recovers rapidly.
Simply moving the individual afflicted with heatstroke to a cooler place is not enough to reverse internal overheating. Emergency medical assistance should be called immediately. While waiting for help to arrive, quick action to lower body temperature must take place. Treatment involves getting the victim to a cool place, loosening clothes or undressing the heat stroke victim, and allowing air to circulate around the body. The next important step is wrapping the individual in wet towels or clothing, and placing ice packs in areas with the greatest blood supply. These areas include the neck, under the arms and knees, and in the groin. The individual can even be placed into a bathtub full of cool water to help speed cooling. A fan can be used to circulate air over dampened skin to simulate sweating and help the cooling process. Once the patient is under medical care, cooling treatments may continue as appropriate. The individual's body temperature will be monitored constantly to guard against overcooling. Breathing and heart rate will be monitored closely, and fluids and electrolytes will be replaced intravenously (IV). Anticonvulsant drugs may be given to help reduce shivering, which warms the body up. After severe heat stroke, bed rest may be recommended for several days.
Prompt treatment for heat cramps is usually very effective, with the individual returning to activity thereafter. Treatment of heat exhaustion usually brings full recovery in one to two days. Heatstroke is a very serious condition and its outcome depends on general health and age. The high internal temperature from heatstroke can cause permanent damage to internal organs, and death is possible.
Because heat cramps, heat exhaustion, and heatstroke are all essentially different levels of severity of the same disorder, the prevention of the onset of all heat disorders is similar. Strenuous exercise should be avoided when it is very hot or humid. Individuals exposed to extreme heat conditions should drink plenty of fluids. Wearing light and loose-fitting clothing in hot weather is important, regardless of the activity. It is important to consume water often and not to wait until thirst develops. If perspiration is excessive, the person should increase fluid intake. When urine output decreases, fluid intake should increase. Eating lightly salted foods can help replace salts lost through perspiration. Ventilation in any working areas in warm weather must be adequate. This can be achieved by simply opening a window or using an electric fan. Proper ventilation promotes adequate sweat evaporation to cool the skin. When heat waves are forecast, families should take care to help prepare or remove elderly people, young children, and others most vulnerable to heat disorders until the extreme heat passes. Children should never be left alone in cars, even when temperatures outside the car seem moderate.
See also Heat (stress) index .
Lopez, Rebecca M. Quick Questions in Heat-related Illness: Expert Advice in Sports Medicine. Thorofare, NJ: Slack, 2015.
McNab, Chris. First Aid Survival Guide. London: Amber Books, 2017.
Krstic, N., et al. “The Heat Exposure Integrated Deprivation Index (HEIDI): a Data-driven Approach to Quantifying Neighborhood Risk During Extreme Hot Weather.” Environment International 109 (2017): 42–52.
Watanabe, T., K. Mizutani, T. Iwai, and H. Nakashima. “Medical Services at an International Summer Camp Event Under Hot and Humid Condition: Experiences from the 23rd World Scout Jamboree, Japan.” Wilderness and Environmental Medicine. Published electronically March 9, 2018. doi: 10.1016/j.wem.2018.01.002. (accessed March 28, 2018).
Centers for Disease Control and Prevention. “Extreme Heat.” http://emergency.cdc.gov/disasters/extremeheat/index.asp (accessed March 28, 2018).
Centers for Disease Control and Prevention. “Heat Stress.” http://www.cdc.gov/niosh/topics/heatstress (accessed March 28, 2018).
Helman, Robert S. “Heatstroke.” Medscape Reference. http://emedicine.medscape.com/article/166320-overview (accessed March 28, 2018).
Scutti, Susan. “How Heat Stroke Kills.” CNN.com . https://www.cnn.com/2017/07/24/health/heat-stroke-explainer/index.html (accessed March 28, 2018).
American College of Sports Medicine, 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 637-9200, Fax: (317) 634-7817, http://www.acsm.org .
Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA, 30333, (404) 639-3534, (800) 232-4636; TTY: (888) 232-6348, email@example.com, http://www.cdc.gov .
Jeffrey P. Larson, RPT
Revised by Teresa G. Odle, BA, ELS