Home > Health & Wellness > Health Library > Heat-Related Illnesses
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.
environmental and physical conditions can make it
hard to stay cool. Heat-related illness is often caused or made worse by
dehydration and fatigue.
Exercising during hot weather, working outdoors, and
overdressing for the environment increase your risk.
Drinking alcohol also increases your risk of dehydration.
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:
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.
Check your symptoms to decide if and when you should see a
Based on your answers, you may need care soon. The
problem probably will not get better without medical care.
Based on your answers, you need
Call911or other emergency services now.
Based on your answers, you may need care right away. The problem is likely to get worse without medical care.
Symptoms of heatstroke may
Heatstroke occurs when the body can't control its own
temperature and body temperature continues to rise.
Some other symptoms of heat-related illness include:
Signs that heat exhaustion is becoming severe include:
If you have symptoms of heat exhaustion, try the following
first aid to cool off:
Severe trouble breathing means:
Moderate trouble breathing means:
Mild trouble breathing means:
Severe trouble breathing means:
Symptoms of difficulty breathing can range from mild to severe. For example:
Symptoms of heat exhaustion may
Heat exhaustion may occur when you are sweating a lot
(typically, while working or exercising in hot weather) and do not drink enough
to replace the fluids you've lost.
Exposure to a hot environment can
cause many problems. Problems can be mild, like a heat rash, swelling in the
hands or feet, or heat cramps. But heat can also lead to more dangerous
situations like confusion, seizures, or passing out.
You have answered all the questions. Based on your answers, you may be
able to take care of this problem at home.
Many things can affect how your body responds to a symptom and what kind
of care you may need. These include:
Based on your answers, you need
While you wait for help to
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:
recognized in the early stages, most heat-related illnesses, such as mild
heat exhaustion, can be treated at home.
If your child is
dehydrated, see the topic
Dehydration for information about home treatment.
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.
Call your doctor if any of the following occur during home
The following tips may help prevent a
heat-related illness. Be aware of the symptoms of heat-related illnesses and
the warning signs of
Staying physically fit can help you
acclimate to 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
To prepare for your appointment, see the topic Making the Most of Your Appointment.
You can help your
doctor diagnose and treat your condition by being prepared to answer the
Other Works Consulted
Lipman GS, et al. (2013). Wilderness Medical Society practice guidelines for the prevention and treatment of heat-related illness. Wilderness and Environmental Medicine, 24(4): 351–361.
Current as of:
June 4, 2014
William H. Blahd, Jr., MD, FACEP - Emergency Medicine & H. Michael O'Connor, MD - Emergency Medicine
How this information was developed to help you make better health decisions.
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