Heat exhaustion is a condition whose symptoms may include heavy
sweating and a rapid pulse, a result of your body overheating. It's one
of three heat-related syndromes, with heat cramps being the mildest and
heatstroke being the most severe.
Causes of heat exhaustion include exposure to high temperatures,
particularly when combined with high humidity, and strenuous physical
activity. Without prompt treatment, heat exhaustion can lead to
heatstroke, a life-threatening condition. Fortunately, heat exhaustion
Your body's heat combined with environmental heat results in what's
called your core temperature — your body's internal temperature. Your
body needs to regulate the heat gain (and, in cold weather, heat loss)
from the environment to maintain a core temperature that's normal,
approximately 98.6 F (37 C).
Your body's failure to cool itself
In hot weather, your body cools itself mainly by sweating. The
evaporation of your sweat regulates your body temperature. However, when
you exercise strenuously or otherwise overexert in hot, humid weather,
your body is less able to cool itself efficiently.As a result, your body may develop heat cramps, the mildest form of
heat-related illness. Signs and symptoms of heat cramps usually include
heavy sweating, fatigue, thirst and muscle cramps. Prompt treatment
usually prevents heat cramps from progressing to heat exhaustion.
You usually can treat heat cramps by drinking fluids or sports drinks
containing electrolytes (Gatorade, Powerade, others), getting into
cooler temperatures, such as an air-conditioned or shaded place, and
Besides hot weather and strenuous activity, other causes of heat exhaustion include:
- Dehydration, which reduces your body's ability to sweat and maintain a normal temperature
- Alcohol use, which can affect your body's ability to regulate your temperature
- Overdressing, particularly in clothes that don't allow sweat to evaporate easily
Anyone can develop heat exhaustion, but certain factors increase your sensitivity to heat. They include:
- Young age or old age. Infants and children
younger than 4 and adults older than 65 are at higher risk of heat
exhaustion. The body's ability to regulate its temperature isn't fully
developed in the young and may be reduced by illness, medications or
other factors in older adults.
- Certain drugs. Medications that affect your
body's ability to stay hydrated and respond appropriately to heat
include some used to treat high blood pressure and heart problems (beta
blockers, diuretics), reduce allergy symptoms (antihistamines), calm you
(tranquilizers), or reduce psychiatric symptoms such as delusions
(antipsychotics). Additionally, some illegal drugs, such as cocaine and
amphetamines, can increase your core temperature.
- Obesity. Carrying excess weight can affect your body's ability to regulate its temperature and cause your body to retain more heat.
- Sudden temperature changes. If you're not used
to the heat, you're more susceptible to heat-related illnesses, such as
heat exhaustion. Traveling to a warm climate from a cold one or living
in an area that's experienced an early heat wave can put you at risk of a
heat-related illness because your body hasn't had a chance to get used
to the higher temperatures.
- A high heat index. The heat index is a single
temperature value that considers how both the outdoor temperature and
humidity make you feel. When the humidity is high, your sweat can't
evaporate as easily and your body has more difficulty cooling itself,
making you prone to heat exhaustion and heatstroke. When the heat index
is 91 F (33 C) or higher, you should take precautions to keep cool.
Untreated, heat exhaustion can lead to heatstroke, a life-threatening
condition that occurs when your body temperature reaches 104 F (40 C)
or higher. Heatstroke requires immediate medical attention to prevent
permanent damage to your brain and other vital organs that can result in
When to see a doctor
If you think you're experiencing heat exhaustion:
- Stop all activity and rest
- Move to a cooler place
- Drink cool water or sports drinks
Contact your doctor if your signs or symptoms worsen or if they don't
improve within one hour. Seek immediate medical attention if your body
temperature reaches 104 F (40 C) or higher.
Tests and diagnosis
If you need medical attention due to heat exhaustion, it may be
apparent to medical personnel that you have heat exhaustion, or they may
take your temperature to confirm the diagnosis and rule out heatstroke.
If your doctors suspect your heat exhaustion may have progressed to
heatstroke, you may need additional tests, including:
- A blood test to check for low blood sodium or potassium and the content of gases in your blood
- A urine test to check the concentration and composition of your urine and to check your kidney function, which can be affected by heatstroke
- Muscle function tests to check for rhabdomyolysis — serious damage to your muscle tissue
- Imaging tests to check for damage to your internal organs
Treatments and drugs
In most cases, you can treat heat exhaustion yourself by doing the following:
- Rest in a cool place. Getting into an
air-conditioned building is best, but at the very least, find a shady
spot or sit in front of a fan. Rest on your back with your legs elevated
higher than your heart level.
- Drink cool fluids. Stick to water or sports drinks. Don't drink any alcoholic beverages, which can contribute to dehydration.
- Try cooling measures. If possible, take a cool shower, soak in a cool bath or put towels soaked in cool water on your skin.
- Loosen clothing. Remove any unnecessary clothing and make sure your clothes are lightweight and nonbinding.
If you don't begin to feel better within one hour of using these
treatment measures, seek prompt medical attention. You may be given
intravenous (IV) fluids to help you rehydrate. Immersing yourself in
cold water, misting your skin, placing yourself in front of fans, or
using cold or ice packs and cooling blankets are some of the techniques
that may be used to bring down your body temperature.
You can take a number of precautions to prevent heat exhaustion and
other heat-related illnesses. When temperatures climb, remember to:
- Wear loose fitting, lightweight, light-colored clothing. Excess, dark or tight clothing holds in heat and doesn't let your body cool properly because it inhibits sweat evaporation.
- Avoid sunburn. If you're going to be outdoors,
wear a lightweight, wide-brimmed hat or use an umbrella to protect
yourself from the sun, and apply sunscreen to any exposed skin. Having a
sunburn reduces your body's ability to rid itself of heat.
- Seek a cooler place. Being in an
air-conditioned building, even for just a few hours, is one of the best
ways to prevent heat exhaustion. If your home doesn't have an air
conditioner, consider spending time at a library or shopping mall. At
the very least, find a well-shaded spot. Fans alone aren't adequate to
counter high heat and humidity.
- Drink plenty of fluids. Staying hydrated will
help your body sweat and maintain a normal body temperature. If your
doctor has told you to limit fluids because of a health condition, be
sure to check with him or her about how much extra you need to drink
when the temperature rises. Avoid alcoholic beverages.
- Take extra precautions with certain medications.
Ask your doctor or pharmacist whether the medications you take make you
more susceptible to heat exhaustion and, if so, what you can do to keep
your body from overheating.
- Avoid hot spots. On a hot day, the temperature
in your parked car can rise 20 F (11 C) in just 10 minutes. Let your car
cool off before you drive it. Never leave children or anyone else in a
parked car in hot weather for any period of time.
- Let your body acclimate to the heat. If you
travel to somewhere hot, or the temperatures suddenly jump in your area,
it can take several weeks for your body to get used to the heat. You'll
still need to take precautions, but working or exercising in heat
should become more tolerable. If you're on vacation, you probably don't
have several weeks to wait, but it's a good idea to wait at least a few
days before attempting vigorous activity in the heat.
It's best not to exercise or do any strenuous activity in hot
weather, but if you must, follow the same precautions and rest
frequently in a cool spot. Taking breaks and replenishing your fluids
during that time will help your body regulate your temperature.
This information is provided by The Mayo Clinic.