Heat disorders are a group of physically related illnesses caused by
prolonged exposure to hot temperatures, restricted fluid intake, or
failure of temperature regulating mechanisms of the body. Disorders of
heat exposure include heat cramps, heat exhaustion, and heat stroke (also
Hyperthermia is the general name given to heat-related illnesses. The two
most common forms of hyperthermia are heat exhaustion and heat stroke, the
latter of which is especially dangerous and requires immediate medical
The thermal regulation centers of the brain help to maintain the
body's internal temperature. Regardless of extreme weather
conditions, the healthy human body keeps a steady temperature of
approximately 98.6°F (37°C). In hot weather or during vigorous
activity, the body perspires. As perspiration evaporates from the skin,
the body is cooled. The thermal regulating centers in the brain help the
body adapt to high temperatures by adjusting the amount of salts
(electrolytes) in the perspiration. Electrolytes help the cells in body
tissues maintain water balance. In hot weather, a healthy body will lose
enough water to cool the body while creating the lowest level of
electrolyte imbalance. If the body loses too much salt and fluid, symptoms
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 with
increased temperature. Individuals exposed to excessive heat should view
heat cramps as a warning sign of 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. Heat exhaustion requires immediate attention, as it can
rapidly progress to heat stroke.
Heat stroke is life threatening, and because a high percentage of
individuals who experience heat stroke
die, immediate medical attention is critical when symptoms first appear.
Heat stroke, like heat exhaustion, is also a result of prolonged exposure
to hot temperatures, restricted fluid intake, or failure of temperature
regulation mechanisms of the body. However, the severity of impact on the
body is much greater with heat stroke.
Heat disorders are harmful to people of all ages, but their severity is
greatest in young children and the elderly. Young children are at risk
because, in relation to their weight, they have a large surface area of
skin through which to lose water. In addition, until about age two,
children's kidneys are not able to concentrate urine and preserve
body fluids as efficiently as adult kidneys. The elderly also often have
reduced kidney function or underlying diseases, or take medications that
make them more vulnerable to dehydration. In healthy adults, heat stroke
and heat exhaustion often affect athletes, firefighters, construction
workers, factory workers, and anyone who exercises heavily and/or wears
heavy clothing in hot, humid weather. Obese individuals and those with
poor circulation or who take medications to reduce excess body fluids
(diuretics) can be at risk when conditions are hot and humid.
Causes and symptoms
Heat cramps are painful
caused by the excessive loss of electrolytes due to heavy perspiration.
The correct balance of electrolytes is crucial to many body functions,
including muscle contraction and nerve impulse transmission. Heavy
exertion in extreme heat and/or restricted fluid intake may lead to heat
With heat cramps, muscle tissue becomes less flexible, causing
, difficult movement, and involuntary tightness. Cramps occurs more often
in the legs and abdomen than in other areas of the body.
Heat exhaustion is caused by exposure to high heat and humidity for many
hours, resulting in excessive loss of fluids and salts through heavy
perspiration. The skin may appear cool, moist, and pale. The child may
, with a feeling of overall weakness and exhaustion.
, faintness, and mental confusion are often present, as is a rapid, weak
pulse. Breathing becomes fast and shallow. Fluid loss reduces blood volume
and lowers blood pressure. Intense thirst and a highly concentrated,
reduced volume of deep yellow or orange urine are signs of inadequate
Before heat stroke occurs, an individual experiences heat exhaustion and
the associated symptoms. When the body can no longer maintain a normal
temperature, heat exhaustion escalates and becomes heat stroke. Heat
stroke is a life-threatening medical emergency that requires immediate
Heat stroke is caused by overexposure to extreme heat, resulting in a
breakdown of the body's heat regulating mechanisms. Body
temperature reaches a dangerous level. An individual with heat stroke has
a body temperature higher than 104°F (40°C), and possibly as
high as 106°F (41.1°C).
Other symptoms of heat stroke include mental confusion with possible
combativeness and bizarre behavior, staggering, and faintness. The pulse
becomes strong and rapid (160–180 beats per minute). The skin takes
on a dry and flushed appearance. There is often very little perspiration.
The individual can quickly lose consciousness or have convulsions.
The doctor should be called when the child shows any symptoms of heat
exhaustion of if he or she has been exposed to heat and dehydrating
conditions and has a body temperature of over 102°F (38.9°C).
Emergency medical services should be called immediately if the individual
has any symptoms of heat stroke or is having difficulty breathing.
Diagnosis of heat cramps usually involves observation of symptoms such as
muscle cramping and thirst. Diagnosis of heat exhaustion or heat stroke,
however, may require a healthcare worker to review the child's
medical history, document symptoms, and obtain blood pressure and
temperature readings. A physician may take blood and urine samples for
further laboratory testing. A test to measure the body's
electrolytes can also give valuable information about chemical imbalances
caused by the heat-related illness.
The care of heat cramps includes placing the child at rest in a cool
environment, while giving cool water with a teaspoon of salt per quart, or
a commercial sports drink (e.g. Gatorade). Usually, rest and liquids are
all that is needed for the child to recover. Mild stretching and massaging
of the muscles may be helpful once the condition improves. The child
should not take salt tablets, because such a high concentration of salt
may actually worsen the condition. When the cramps stop, the person
usually can begin light activity again if there are no other signs of
illness. The child needs to continue drinking fluids and should be watched
carefully for further signs of heat-related illnesses.
The child suffering from heat exhaustion should stop all physical activity
and move immediately to a cool place out of the sun, preferably a cool,
air-conditioned location. He or she should lay 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 is usually all the treatment that is needed, and
is rarely required. Following rehydration, the child usually recovers
Simply moving the individual experiencing heat stroke 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.
Immediate treatment involves getting the child to a cool place, loosening
clothing or undressing the person, and allowing air to circulate around
the body. The next step is to wrap the child in wet towels or clothing,
and place ice packs in areas with the greatest blood supply. These areas
include the neck, under the arm and knees, and in the groin. Once the
patient is under medical care, cooling treatments continue as appropriate.
The child's body temperature is monitored constantly to guard
against overcooling. Breathing and heart rate are monitored, and fluids
and electrolytes are replaced intravenously. Anti-convulsant drugs may be
given. After severe heat stroke, hospitalization may be necessary and bed
rest is recommended for several days.
Prompt treatment for heat cramps is usually very effective, allowing the
individual to return rapidly to activity. Treatment of heat exhaustion
usually brings full recovery in one to two days. Heat stroke is a very
serious condition and its outcome depends upon the general health and age
of the individual. Due to the high body temperature resulting from heat
stroke, permanent damage to the brain, kidneys, heart, and other internal
organs is possible. Heat stroke can be fatal, especially for infants and
Because heat cramps, heat exhaustion, and heat stroke have a cascade
effect, the prevention of the onset of all heat disorders is similar.
Parents need to be especially alert to dehydration and the development of
heat disorders in infants who cannot ask for something to drink. Parents
need to take the initiative in encouraging children to drink frequently in
hot weather. Water or sports drinks are a better choice of liquids than
Before the 1970s, some coaches felt it was good training to limit the
amount of fluids athletes drank at practices. As a result, there were 39
documented heat-related deaths in athletes between 1964 and 1973. As the
water-electrolyte balance of the body became better understood, most
coaches have recognized that water should be freely available during
athletic practices and events. As a result, documented heat-related deaths
declined substantially in the 1980s. When children participate in
athletics, parents need to be aware of the potential for heat disorders
and assure that appropriate measures for prevention are taken by coaches.
—Also termed seizures; a sudden violent contraction of a group of
—Salts and minerals that produce electrically charged particles
(ions) in body fluids. Common human electrolytes are sodium chloride,
potassium, calcium, and sodium bicarbonate. Electrolytes control the
fluid balance of the body and are important in muscle contraction,
energy generation, and almost all major biochemical reactions in the
—The restoration of water or fluid to a body that has become
American Red Cross.
Standard First Aid.
St. Louis: Mosby Year Book, 1993.
Larson, David E., ed.
Mayo Clinic Family Health Book.
3rd ed. New York: HarperResource, 2003.
Mellion, Morris B. et al.
The Team Physicians Hand Book.
Philadelphia: Hanley & Belfus, 2001.
"The Life Secretariat: Heat Disorders."
United States Air Force.
Available online at"
http://www.mindef.gov.sg/life/heatd.htm (accessed March 3, 2005).