A healthy body temperature is maintained by
the nervous system. As the body temperature increases, the
body tries to maintain its normal temperature by
transferring heat. Sweating and
blood flow to the skin (thermoregulation) help us keep our
bodies cool. A heat-related illness occurs when our bodies can no longer
transfer enough heat to keep us cool.
A high body temperature
(hyperthermia) can develop rapidly in extremely hot
environments, such as when a child is left in a car in the summer heat. Hot
temperatures can also build up in small spaces where the ventilation is poor,
such as attics or boiler rooms. People working in these environments may
quickly develop hyperthermia.
High temperature caused by a
fever is different from a high body temperature caused
by a heat-related illness. A fever is the body's normal reaction to infection
and other conditions, both minor and serious. Heat-related illnesses produce a
high body temperature because the body cannot transfer heat effectively or
because external heat gain is excessive.
Heat rash (prickly heat), which occurs when the
sweat ducts to the skin become blocked or swell, causing discomfort and
Heat cramps, which occur in muscles after exercise
because sweating causes the body to lose water, salt, and minerals (electrolytes).
Heat edema (swelling) in the legs and hands, which can occur when
you sit or stand for a long time in a hot environment.
(hyperventilation and heat stress), which is usually caused by short periods of
stress in a hot environment.
(fainting), which occurs from low blood pressure when heat causes the blood
vessels to expand (dilate) and body fluids move into the legs because of
Heat exhaustion (heat prostration), which generally
develops when a person is working or exercising in hot weather and does not
drink enough liquids to replace those lost liquids.
Heatstroke (sunstroke), which occurs when the body
fails to regulate its own temperature and body temperature continues to rise,
often to 105°F (40.6°C) or
higher. Heatstroke is a medical emergency. Even with immediate treatment, it can be life-threatening or cause serious long-term problems.
medicines increase your risk of a heat-related
illness. Some medicines decrease the amount of blood pumped by the heart
(cardiac output) and limit blood flow to the skin, so your body is less able to
cool itself by sweating. Other medicines can alter your sense of thirst or
increase your body's production of heat. If you take medicines regularly, ask
your doctor for advice about hot-weather activity and your risk of getting a
Other things that may increase your risk of
a heat-related illness include:
Age. Babies do not lose heat quickly and they do
not sweat effectively. Older adults do not sweat easily and usually have other
health conditions that affect their ability to lose heat.
Obesity. People who are overweight have decreased
blood flow to the skin, hold heat in because of the insulating layer of fat
tissue, and have a greater body mass to cool.
Heat waves. People who live in cities are especially vulnerable to illness
during a heat wave because heat is trapped by tall buildings and air
pollutants, especially if there is a high level of
Chronic diseases, such as
heart failure, and cancer. These conditions change the
way the body gets rid of heat.
Travel to wilderness areas or
foreign countries with high outdoor temperatures and humidity. When you go to a
different climate, your body must get used to the differences (acclimate) to keep your body temperature in a normal
Most heat-related illnesses can be prevented by keeping the
body cool and by avoiding dehydration in hot environments. Home treatment is
usually all that is needed to treat mild heat-related illnesses. Heat
exhaustion and heatstroke need immediate medical treatment.
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Emergency first aid
Emergency first aid for
heatstroke is needed immediately because this
condition is life-threatening. After calling
911 or other emergency medical services,
follow these first aid steps:
Move the person into a cool place, out of
Remove the person's unnecessary clothing and place
the person on his or her side to expose as much skin surface to the air as
Cool the person's entire body by sponging or spraying
cool (not cold) water, and fan the person to lower the person's body
temperature. Watch for signs of
rapidly progressing heatstroke, such as seizure, unconsciousness for longer than a few seconds, and moderate to severe difficulty breathing.
packs on the groin, neck, and armpits, where large blood vessels lie close to
the skin surface. Do not immerse the person in an ice
Check the person's rectal temperature, and try to cool
it to 102°F (39°C) or lower as
soon as possible. The longer the body is at a high temperature, the more
serious the illness and the more likely it is that complications will develop.
Temperatures taken by mouth or in the ear are not
accurate in this emergency situation.
Do not give any medicine to reduce a high body temperature that can
occur with heatstroke. Medicines may cause problems because of the body's
response to heatstroke.
If the person is awake and
alert enough to swallow, give the person fluids [32 fl oz (1 L) to
64 fl oz (2 L) over 1 to 2
hours] for hydration. Most people with heatstroke have an altered level of
consciousness and cannot safely be given fluids to drink. You may have to help.
Make sure the person is sitting up enough so that he or she does not choke.
Home treatment for mild heat-related illness
recognized in the early stages, most heat-related illnesses, such as mild
heat exhaustion, can be treated at home.
Stop your activity, and rest.
out of direct sunlight and lie down in a cooler environment, such as shade or
an air-conditioned area. Elevate your feet. Remove all unnecessary
Cool down by applying cool compresses or having a fan
blow on you. Place
ice bags under your arms and in your groin area, where large blood vessels
lie close to the skin surface, to cool down quickly.
rehydration drinks, juices, or water to replace
2 qt (2 L) of cool fluids over
2 to 4 hours. You are drinking enough fluids if your urine is normal in color
and amount and you are urinating every 2 to 4 hours. Total rehydration with
oral fluids usually takes about 36 hours, but most people will begin to feel
better within a few hours.
Rest for 24 hours,
and continue fluid replacement with a rehydration drink. Rest from any
strenuous physical activity for 1 to 3 days.
Heat syncope (fainting) usually does not last long and
improves when you lie down to a flat position. It is helpful to lie in a cooler
Heat edema (swelling) is treated with
rest and by elevating your legs. If you are standing for a long time in a hot
environment, flex your leg muscles often so that blood does not pool in your
lower legs, which can lead to heat edema and fainting.
Heat cramps are
treated by getting out of the heat and replacing fluids and salt. If you are
not on a salt- (sodium-) restricted diet, eat a little more salt, such as a few
nuts or pretzels. Do not use salt tablets, because they
are absorbed slowly and can cause irritation of the stomach. Try massaging and
stretching your cramped muscles.
Heat rash (prickly heat) usually
gets better and goes away without treatment.
Antihistamines may help if you are having problems
with itching. Keep areas clean and dry to help prevent a skin infection. Do not
use baby powder while a rash is present. The powder can build up in the skin
creases and hold moisture, allowing the growth of bacteria that may cause
infection. Dress in as few clothes as possible during hot weather. Keep your
home, especially sleeping areas, cool.
The following tips may help prevent a
heat-related illness. Be aware of the symptoms of heat-related illnesses and
the warning signs of
heat safety measures when you are physically active in
hot weather. This is especially important for outdoor workers and military
personnel. Avoid strenuous activity in hot, humid weather or during the hottest
part of the day (between 10 a.m. and 4 p.m.). Use caution during your physical
activity in the heat if you have
Drink plenty of water
before, during, and after you are active. This is very important when it's hot
out and when you do intense exercise.
Fluids such as
rehydration drinks, juices, or water help replace lost
fluids, especially if you sweat a lot.
Drink on schedule. Two hours before
24 fl oz (750 mL) of fluid.
Drink 16 fl oz (500 mL) of
fluid 15 minutes before exercising. Continue drinking
8 fl oz (250 mL) of fluid every
15 minutes while exercising.
rehydration drinks, which are absorbed as quickly as water but
also replace sugar, sodium, and other nutrients. Eat fruits and vegetables to
Check your urine. Urine should be clear to pale
yellow, and there should be a large amount if you are drinking adequately. You
should urinate every 2 to 4 hours during an activity when you are staying
properly hydrated. If your urine output decreases, drink more fluids.
Do not spend much time in the sun. If possible,
exercise or work outside during the cooler times of the day. Wear lightweight,
clothing in hot weather, so your skin can cool through
evaporation. Wear a wide-brimmed hat or use an umbrella for
Stay cool as much as possible. Take frequent breaks in the
shade, by a fan, or in air-conditioning. Cool your skin by spraying water over
your body. Take a cool bath or shower 1 or 2 times a day in hot
If you have to stand for any length of time in a hot
environment, flex your leg muscles often while standing. This prevents blood
from pooling in your lower legs, which can lead to fainting. To prevent
swelling (heat edema), wear support hose
to stimulate circulation while standing for long periods of time.
Do not drink caffeine or alcohol. They
increase blood flow to the skin and increase your risk of dehydration.
Staying physically fit can help you
acclimate a hot environment. Before you travel to or
work in a hotter environment, use gradual physical conditioning. This takes
about 8 to 14 days for adults. Children require 10 to 14 days for their bodies
to acclimate to the heat. If you travel to a hot environment and are not
accustomed to the heat, cut your usual outside physical activities in half for
the first 4 to 5 days. Gradually increase your activities after your body
adjusts to the heat and level of activity.
Be aware that when the
outdoor humidity is greater than 75%, the body's ability to lose heat by
sweating is decreased. Other ways of keeping cool need to be used. The
National Weather Service lists a
heat index each day in the newspaper to alert people
of the risk for a heat-related illness in relation to the air temperature and
humidity of that day. Direct exposure to the sun can increase the risk of a
heat-related illness on days when the heat index is high.
who have had heatstroke in the past may be more sensitive to the effects of
heat in the first few months following the illness, but they do not have
How this information was developed to help you make better health decisions.