Heat-related illness (hyperthermia) facts
- Hyperthermia is overheating of the body.
- Heat-related illness occurs as a result of heat exposure.
- Heat-related illnesses include
- Heat stroke is the most severe form of heat-related illness, and requires immediate medical attention.
- Certain individuals, such as the elderly, infants and young children, the obese, outdoor workers, and those with chronic medical conditions are at increased risk for developing heat-related illness.
- Signs and symptoms of heat-related illness vary based on the condition, but may include
- Treatment for heat-related illness generally includes moving the individual out of the hot environment, implementing cooling measures as needed, rest, and rehydration.
- Prevention of heat-related illness is best accomplished through proper planning and preparation, such as increasing fluid intake, wearing appropriate clothing and sunscreen, remaining in a cool environment, acclimating yourself to the hot environment, and using common sense.
What is a heat-related illness?
A heat-related illness is a medical condition that may occur as a result of heat exposure. Even short periods of high temperatures can cause serious health problems. Heat-related illness encompasses a spectrum of conditions that range from minor illnesses to life-threatening medical emergencies. There are several heat-related illnesses, including heat stroke, heat exhaustion, heat cramps, heat syncope (fainting), and heat rash.
Summer can bring heat waves with unusually high temperatures that can last for days and sometimes weeks.
- According to statistics from the Centers for Disease Control and Prevention
(CDC), there were
7,415 death due to heat-related illness in the United States from 1999 to 2010, or an average of approximately
618 death per year.
- Heat waves lead to more deaths annually in the United States than tornadoes,
earthquakes, floods, and
- In the summer of 1980, a severe heat wave hit the United States, and
approximately 1,700 people lost their lives from heat-related illness; and
in the summer of 2003, tens of thousands of people died in Europe from an extreme heat wave.
- The summer of 2012 heat wave in the United States led to many heat-related deaths, and numerous all-time high temperature records
were broken throughout the United States.
- Most recently, a summer heat wave in Pakistan in 2015 led to more than 1,000 fatalities.
- High temperatures put people at risk.
Quick GuideDehydration: Causes, Symptoms & Tips to Stay Hydrated
Did You Know You Could Die From a Heat-Related Illness?
5 Ways to Recognize a Heat-Related Illness
In all heat-related illnesses, the symptoms appear when a person is exposed
to extreme temperatures. The following checklist can help you recognize the
symptoms of heat-related illnesses:
- Heat Rash: Heat rash looks like a red cluster of pimples or
- Heat cramps: Symptoms are painful muscle
spasms in the arms, legs, or abdomen
- Heat syncope (fainting): Symptoms of heat syncope or fainting are
- Heat exhaustion is a warning that the body is getting too hot.
- Heat stroke is a serious, life-threatening condition that occurs when the body loses its ability to control its temperature.
What causes a heat-related illness?
People suffer heat-related illness when the body's normal temperature control system is unable to effectively regulate its internal temperature. Normally, at high temperatures the body primarily cools itself through the evaporation of sweat. However, under certain conditions (air temperatures above 95 F/35 C high humidity), this cooling mechanism becomes less effective. When the humidity is high, sweat will not evaporate as quickly, preventing the body from releasing heat quickly. Furthermore, without adequate fluid intake, excessive fluid losses and
electrolyte imbalances may also occur leading to dehydration. In such cases, a person's body temperature rises rapidly. Very high body temperatures can damage the brain and other vital organs.
Picture of the layers of the skin including the sweat glands
Other conditions that can limit the ability to regulate body temperature include old age,
obesity, fever, dehydration, heart disease, poor circulation, sunburn, and drug or alcohol use.
Who is at risk of heat-related illness?
Those at greatest risk of heat-related illness include:
- infants and
children up to four years of age,
- people 65 years of age or older,
- people who are overweight,
- people who overexert during outdoor work or exercise,
- people with mental illness, and
- people who are chronically ill or on certain medications.
Infants and children up to four years of age are very sensitive to the effects of high temperatures and rely on others to regulate their environment and
to provide adequate fluid intake.
Moreover, they have a higher metabolic rate and inefficient sweating compared to
People 65 years of age or older may not compensate for heat stress efficiently, and are less likely to sense and respond to changes in temperature.
The elderly population also is at a higher risk because they usually have other
pre-existing medical conditions, and they often take medications that can make
them more vulnerable to dehydration (for example, diuretics).
Overweight individuals may be prone to heat-related illness because of their tendency to retain more body heat.
Any health condition that causes dehydration makes the body more susceptible to heat-related illness. If you or someone you know is at higher risk, it is important to drink plenty of fluids, avoid overexertion, and get your doctor or pharmacist's advice about medications being taken for:
What are the symptoms of heat-related illness?
Signs and symptoms of heat-related illness vary based on the severity of the
- Heat rash symptoms: red bumps on the skin, a feeling of prickly
or itchy skin.
- Heat syncope (fainting) symptoms: dizziness or lightheadedness and
fainting, generally due to prolonged exposure to heat, dehydration, or
- Heat cramps symptoms: significant sweating, involuntary spasms of
the muscles in the body, most often affecting the legs.
- Heat exhaustion symptoms: nausea and vomiting, headache, muscle
cramps, weakness, and profuse sweating.
- Heat stroke symptoms: dizziness, muscle cramps and aches,
nausea and vomiting,
fatigue, headache, weakness,
confusion and coma. Heat stroke is a medical
Heat stroke is a medical emergency requiring immediate medical attention. It is the most severe form of heat-related illness, and it can sometimes lead to death or permanent disability. Heat stroke occurs when the body's ability to regulate its internal temperature has failed. The body's temperature rises rapidly in excess of 104 F
(40. C), leading to damage to the brain and other vital organs. Generally, the extent of injury depends on the duration of exposure to excessive heat and the peak temperature attained. Heat stroke is sometimes referred to as sunstroke.
Heat stroke can be categorized as either exertional heat stroke (EHS) or
nonexertional heat stroke (NEHS). Exertional heat stroke generally occurs in young, healthy individuals who engage in strenuous activity in hot weather. Nonexertional heat stroke (also referred to as classic heat stroke) typically occurs in the elderly, the very young, or the chronically ill.
What are the signs and symptoms of heat stroke?
Warning signs of heat stroke vary but
- high body temperature (above 104 F or 40 C),
- skin that is red, hot, and either moist or dry (sweating may have
- rapid heart rate,
- difficulty breathing,
- loss of coordination,
- nausea and vomiting,
- confusion and
- seizures, and
What is the treatment for heat stroke?
If you see any of these signs, you may
be dealing with a life-threatening emergency. Have someone call for immediate
medical assistance while you begin cooling the affected individual:
- Get the person to a cool indoor or outdoor area and remove restrictive
- Cool the person rapidly using whatever methods
you can. For example, if possible, immerse the person in a tub of cool water or place
them in a cool shower. You may also spray them with lukewarm water and blow cool
air from a fan towards them. If the humidity is low, loosely wrap the person's
body in a cool, wet sheet and fan him or her vigorously. Alternatively, place
ice or cold packs to the armpits, neck, and groin areas.
- Monitor body
temperature, and continue cooling efforts until the body temperature drops to
about 102 F or lower (38.8 C), in order to prevent overcooling the affected
- If emergency medical personnel are delayed, call the
hospital emergency room for further instructions.
- If the affected individual is awake and alert, give them cool fluids to drink. Do not give
them alcohol to drink.
If the affected individual's muscles begin to twitch
uncontrollably (seizure) as a result of heat stroke; keep the individual from injuring themselves,
and do not place any object in the mouth and do
not give fluids. If there is vomiting, make sure the airway remains clear by
turning the person on their side to prevent choking.
Heat cramps usually affect people who sweat significantly during
strenuous activity. This sweating depletes the body's salt and moisture. The low
salt level in the muscles causes painful muscle cramps, often following exercise. Heat cramps may also be a
symptom of heat exhaustion.
What are the signs and symptoms of heat cramps?
Heat cramps are muscle pains or muscle spasms (usually in the abdomen, arms, or legs) that may occur in association with strenuous activity. If
the affected person has heart problems or are
on a low sodium diet, seek medical attention for heat cramps.
What is the treatment for heat cramps?
- Stop all activity, and sit and rest in a cool place.
- Drink water or a sports beverage, and eat a salty snack.
- Passively stretch the affected muscles.
- Do not return to strenuous activity for a few hours after the cramps have subsided
as further exertion can lead to heat exhaustion or rarely, heat stroke.
- Seek medical attention for heat cramps if they do not subside in 1 hour.
Heat exhaustion is the body's response to an excessive loss of water and salt contained in sweat as a result of engaging in physical activity (work or exercising) in a hot environment. The body temperature may be normal or mildly elevated, but not above 104 F
(40 C). It often occurs in individuals who are not accustomed to working or exercising in the heat. The symptoms may range from minor complaints to more pronounced symptoms, however the
affected individual will not experience the central nervous system manifestations noted with heat stroke. Many cases of heat exhaustion can be treated outside of the hospital setting however it is important to understand that heat exhaustion can progress to heat stroke if not properly addressed in a timely fashion.
What are the signs and symptoms of heat exhaustion?
Warning signs of heat exhaustion include:
- a normal or mildly elevated body temperature,
- heavy sweating,
- pallor (paleness),
- muscle cramps and muscle
- dizziness and lightheadedness,
- headache, and
The skin may
be cool and moist. The affected individual's pulse rate may be fast, and breathing
may be fast and shallow. If heat exhaustion is untreated and heat exposure
continues, it may sometimes progress to
What is the treatment for heat exhaustion?
Cooling measures that may be effective include:
- drink cool, non-alcoholic beverages, such as water and sports drinks,
- eat salty snacks,
- rest in the shade or in an air-conditioned environment,
- take a cool shower or bath, and
- loosen or remove restrictive clothing.
Seek medical attention immediately if:
- the symptoms are severe or worsening, or
- the affected individual has serious underlying health problems (for example, heart
disease or diabetes).
Otherwise, help the person cool
off, and seek medical attention if symptoms worsen or last longer than one hour.
Heat syncope (fainting)
Heat syncope is a fainting episode that occurs in the heat, either during
prolonged standing or exercise, or when rapidly standing from a lying or sitting
position. It typically occurs in individuals who are not acclimatized to the
heat. Dehydration can also contribute to this condition.
What are the signs and symptoms of heat syncope?
- dizziness or lightheadedness, and
What is the treatment for heat syncope?
- Sit and rest in a cool place. The affected individual may also lie down and elevate
the legs above the level of the heart.
- Drink water or a sports beverage.
- Seek immediate medical attention for repeated episodes of fainting, or if the individual experiences chest pain,
Heat rash is a skin irritation that occurs in hot, humid weather. It is caused by profuse sweating, which can lead to the blockage of sweat ducts. It can occur at any age, but is most common in young children.
What are the signs and symptoms of heat rash?
Heat rash appears as a cluster of small red pimples or blisters. This skin irritation can be itchy. It typically occurs on the neck and upper chest, in the groin, under the breasts, and in
the elbow creases.
Pictures of heat rash in children and adults
What is the treatment for heat rash?
The best treatment for heat rash is to avoid a hot, humid environment and to try to remain in cooler, less humid conditions. Try to keep the affected area dry, and wear light, loose clothing. Dusting powder may be used to increase comfort, but avoid using ointments or creams because they keep the skin warm and moist and may make the condition worse.
Treating heat rash is simple and usually does not require medical
Heat-related illness prevention
To protect your health when temperatures are extremely high, remember to keep
cool and use common sense. The following tips are important.
Drink plenty of fluids
Increase your fluid intake regardless of your activity level. Do not wait
until you feel thirsty. During heavy
exercise in a hot environment, drink 2-4 glasses (16-32 ounces) of cool fluids
Caution: If your doctor has prescribed a fluid-restricted diet or diuretics
for you, ask your doctor how much you should drink.
- During hot weather, you will need to drink more liquid than your thirst
indicates. This is especially true for
people 65 years of age and older who
often have a decreased ability to respond to external temperature changes.
- Drinking plenty of liquids during exercise is especially important. However,
avoid very cold beverages because they can cause
- In addition,
avoid drinks containing alcohol or caffeine, because they will actually cause you to lose
Replace salt and minerals
Heavy sweating removes salt and minerals from the body. These are necessary
for your body and must be replaced. The easiest and safest way to replace salt
and minerals is through your diet.
- Drink a sports beverage during
exercise or work in the heat.
- Do not take salt tablets unless directed by
- If you are on a low-salt diet, ask your doctor before changing what
you eat or drink, especially before drinking sports beverages.
Wear appropriate clothing and sunscreen
- Wear as little clothing as possible when you are at home. Choose lightweight,
light-colored, loose-fitting clothing. In the hot sun, a wide-brimmed hat will
provide shade and keep the head cool.
- Sunburn affects the body's ability to cool itself and causes a loss of body
fluids. It also causes pain and damages the skin.
- A variety of sunscreens are available to reduce the risk of sunburn. The
protection that they offer against sunburn varies. Check the sun protection
factor (SPF) number on the label of the sunscreen container. Select SPF 15 or
higher to protect yourself adequately. Apply sunscreen 30 minutes before going
outdoors and reapply according to package directions.
- If you are unaccustomed to working or exercising in a hot environment, start
slowly and pick up the pace gradually.
- If exertion in the heat makes your heart
pound and leaves you gasping for breath, STOP all activity. You should get into a cool
area or in the shade, and rest, especially if you become lightheaded,
weak, or faint.
Stay cool indoors
- The most efficient way to beat the heat is to stay in a cool or air-conditioned
- If you do not have an air conditioner or evaporative cooling unit,
consider a visit to a shopping mall, see a movie in a movie theater, or visit a public library for a few hours.
your local health department to see if there are any heat-relief shelters in
- Electric fans may be useful to increase comfort and to draw cool air
into your home at night, but do not rely on a fan as your primary cooling device
during a heat wave. When the temperature is in the 90s or higher, a fan will not
prevent heat-related illness.
- A cool shower or bath is a more effective way to
cool off. Also, use your stove and oven less to maintain a cooler temperature in
Schedule outdoor activities carefully
- If you must be out in the heat, try to plan your activities so that you are
outdoors either before noon or in the evening.
- While outdoors, rest frequently
in a shady area.
- Resting periodically will give your body's thermostat a chance
Use a buddy system
- When working in the heat, monitor the condition of your coworkers and have
someone do the same for you. Heat-related illness can cause a person to become
confused or lose consciousness.
- During a heat wave, have a friend or relative
call to check in on you twice a day if you are 65 years of age or older. If you
know anyone in this age group, check on them at least twice a day.
Adjust to the environment
- Be aware that any sudden change in temperature, such as an early summer heat
wave, will be stressful to your body. You will have a greater tolerance for the
heat if you limit your physical activity until you become accustomed to the
- If traveling to a hotter climate, allow several days to become acclimated
before attempting any vigorous exercise, and work up to it gradually.
Use common sense
- Avoid hot foods and heavy meals as they may add heat to your body.
- Do not
ever leave infants, children, or pets in a parked car.
- Dress infants and young
children in cool, loose clothing and shade their heads and faces with hats or an
umbrella. Make sure they use sunscreen when outdoors.
- Limit sun exposure during the mid-day hours and in places of potential
heavy sun exposure, such as beaches.
- Ensure that infants and children drink adequate
amounts of liquids.
- Make sure to keep your pet cool by giving them plenty of fresh water, and leave the water in
a shady area.
One last hot tip
These self-help measures are not a substitute for medical care but may help
you recognize and respond promptly to warning signs of trouble. Your best
defense against heat-related illness is prevention. Staying cool and making
simple changes in your fluid intake, activities, and clothing during hot weather
can help you remain safe and healthy.
Quick GuideDehydration: Causes, Symptoms & Tips to Stay Hydrated
Medically Reviewed on 10/6/2016
Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine
Centers for Disease Control and Prevention. Extreme Heat. <http://emergency.cdc.gov/disasters/extremeheat/index.asp>