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Heat-Related Illnesses

Topic Overview

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-related illnesses include:

  • Heat rash (prickly heat), which occurs when the sweat ducts to the skin become blocked or swell, causing discomfort and itching.
  • 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.
  • Heat tetany (hyperventilation and heat stress), which is usually caused by short periods of stress in a hot environment.
  • Heat syncope (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 gravity.
  • 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.

Often, 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.

Many 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 heat-related illness.

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 humidity.
  • Chronic diseases, such as diabetes, 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 range.

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 doctor.

Check Your Symptoms

Do you have a heat-related illness?
Yes
Heat-related illness
No
Heat-related illness
How old are you?
Less than 12 years
Less than 12 years
12 years or older
12 years or older
Are you male or female?
Male
Male
Female
Female
Did you pass out completely (lose consciousness)?
Yes
Lost consciousness
No
Lost consciousness
If you are answering for someone else: Is the person unconscious now?
(If you are answering this question for yourself, say no.)
Yes
Unconscious now
No
Unconscious now
Are you back to your normal level of alertness?
After passing out, it's normal to feel a little confused, weak, or lightheaded when you first wake up or come to. But unless something else is wrong, these symptoms should pass pretty quickly and you should soon feel about as awake and alert as you normally do.
Yes
Has returned to normal after loss of consciousness
No
Has returned to normal after loss of consciousness
Did the loss of consciousness occur during the past 24 hours?
Yes
Loss of consciousness in past 24 hours
No
Loss of consciousness in past 24 hours
Have you had a seizure?
Yes
Seizure
No
Seizure
Yes
Heatstroke symptoms
No
Heatstroke symptoms
Are you having trouble breathing (more than a stuffy nose)?
Yes
Difficulty breathing more than a stuffy nose
No
Difficulty breathing more than a stuffy nose
Would you describe the breathing problem as severe, moderate, or mild?
Severe
Severe difficulty breathing
Moderate
Moderate difficulty breathing
Mild
Mild difficulty breathing
Yes
Heat exhaustion symptoms
No
Heat exhaustion symptoms
Yes
Severe symptoms of heat exhaustion
No
Severe symptoms of heat exhaustion
Did you faint?
Yes
Fainted
No
Fainted
Have you tried first aid for more than 1 hour?
Yes
First aid for more than 1 hour
No
First aid for more than 1 hour
Do you still have symptoms despite doing first aid?
Yes
Symptoms have persisted despite first aid
No
Symptoms have improved with first aid
Yes
Other symptoms of heat-related illness
No
Other symptoms of heat-related illness
Have you tried home treatment for more than 4 hours?
Home treatment includes resting, staying out of the heat and sun, using cool compresses or a fan to cool off, and drinking plenty of fluids.
Yes
Home treatment for more than 4 hours
No
Home treatment for more than 4 hours

Many things can affect how your body responds to a symptom and what kind of care you may need. These include:

  • Your age. Babies and older adults tend to get sicker quicker.
  • Your overall health. If you have a condition such as diabetes, HIV, cancer, or heart disease, you may need to pay closer attention to certain symptoms and seek care sooner.
  • Medicines you take. Certain medicines, herbal remedies, and supplements can cause symptoms or make them worse.
  • Recent health events, such as surgery or injury. These kinds of events can cause symptoms afterwards or make them more serious.
  • Your health habits and lifestyle, such as eating and exercise habits, smoking, alcohol or drug use, sexual history, and travel.

Seek Care Now

Based on your answers, you may need care right away. The problem is likely to get worse without medical care.

  • Call your doctor now to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, seek care in the next hour.
  • You do not need to call an ambulance unless:
    • You cannot travel safely either by driving yourself or by having someone else drive you.
    • You are in an area where heavy traffic or other problems may slow you down.

Call 911 Now

Based on your answers, you need emergency care.

Call911or other emergency services now.

Seek Care Today

Based on your answers, you may need care soon. The problem probably will not get better without medical care.

  • Call your doctor today to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, seek care today.
  • If it is evening, watch the symptoms and seek care in the morning.
  • If the symptoms get worse, seek care sooner.

Signs that heat exhaustion is becoming severe include:

  • Blurred vision.
  • Fast breathing and fast heart rate (more than 120 beats per minute when you are at rest).
  • Severe belly cramps.
  • Very heavy sweating (sweat is pouring off you and soaking through your clothes).

Call 911 Now

Based on your answers, you need emergency care.

Call911or other emergency services now.

While you wait for help to arrive:

  • Spray or sponge the person with cool water. Do not put the person in an ice bath.
  • Use ice packs on the neck, armpits, and groin.
  • Do not use any medicine (such as aspirin, acetaminophen, or ibuprofen) to reduce the person's temperature.

Symptoms of difficulty breathing can range from mild to severe. For example:

  • You may feel a little out of breath but still be able to talk (mild difficulty breathing), or you may be so out of breath that you cannot talk at all (severe difficulty breathing).
  • It may be getting hard to breathe with activity (mild difficulty breathing), or you may have to work very hard to breathe even when you’re at rest (severe difficulty breathing).

Symptoms of heat exhaustion may include:

  • Weakness, dizziness, or fatigue.
  • Headache.
  • Nausea.
  • Skin that is pale, cool, and moist. 
  • Raised body temperature.

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.

Symptoms of heatstroke may include:

  • Feeling or acting very confused, restless, or anxious.
  • Trouble breathing.
  • Sweating heavily, or not sweating at all (sweating may have stopped).
  • Skin that is red, hot, and dry, even in the armpits.
  • Passing out.
  • Seizure.

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:

  • Muscle twitching or spasms.
  • Muscles that feel hard and lumpy.
  • Sore muscles.

Try Home Treatment

You have answered all the questions. Based on your answers, you may be able to take care of this problem at home.

  • Try home treatment to relieve the symptoms.
  • Call your doctor if symptoms get worse or you have any concerns (for example, if symptoms are not getting better as you would expect). You may need care sooner.

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.

If you have symptoms of heat exhaustion, try the following first aid to cool off:

  • Stop what you are doing and rest.
  • Get out of the sun and heat.
  • Remove any extra clothing.
  • Spray or mist the body with cool water.
  • Use a fan if one is available.
  • Drink plenty of cool water or rehydration drinks.

Severe trouble breathing means:

  • You cannot talk at all.
  • You have to work very hard to breathe.
  • You feel like you can't get enough air.
  • You do not feel alert or cannot think clearly.

Moderate trouble breathing means:

  • It's hard to talk in full sentences.
  • It's hard to breathe with activity.

Mild trouble breathing means:

  • You feel a little out of breath but can still talk.
  • It's becoming hard to breathe with activity.

Severe trouble breathing means:

  • The child cannot eat or talk because he or she is breathing so hard.
  • The child's nostrils are flaring and the belly is moving in and out with every breath.
  • The child seems to be tiring out.
  • The child seems very sleepy or confused.

Moderate trouble breathing means:

  • The child is breathing a lot faster than usual.
  • The child has to take breaks from eating or talking to breathe.
  • The nostrils flare or the belly moves in and out at times when the child breathes.

Mild trouble breathing means:

  • The child is breathing a little faster than usual.
  • The child seems a little out of breath but can still eat or talk.

Home Treatment

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 direct sunlight.
  • 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 possible.
  • 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.
  • Apply ice 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 bath.
  • 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.
  • If a person has stopped breathing, begin CPR.
  • 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

When recognized in the early stages, most heat-related illnesses, such as mild heat exhaustion, can be treated at home.

  • Stop your activity, and rest.
  • Get 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 clothing.
  • 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.
  • Drink rehydration drinks, juices, or water to replace fluids. Drink 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.

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 environment.

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.

Symptoms to watch for during home treatment

Call your doctor if any of the following occur during home treatment:

  • A seizure occurs.
  • Decreased mental alertness develops.
  • Shortness of breath develops.
  • Symptoms become more severe or frequent.

Prevention

The following tips may help prevent a heat-related illness. Be aware of the symptoms of heat-related illnesses and the warning signs of dehydration.

  • Practice 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 health risks.
  • 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 exercising, drink 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.
    • Drink rehydration drinks, which are absorbed as quickly as water but also replace sugar, sodium, and other nutrients. Eat fruits and vegetables to replace nutrients.
    • 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, light-colored, loose-fitting clothing in hot weather, so your skin can cool through evaporation. Wear a wide-brimmed hat or use an umbrella for shade.
  • 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 weather.
  • If you have to stand for any length of time in a hot environment, flex your leg muscles often. 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 alcohol. It increases blood flow to the skin and increases your risk of dehydration.

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.

People 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 long-term problems.

Preparing For Your Appointment

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 following questions:

  • What are your main symptoms?
  • How long have you had your symptoms? How severe are they?
  • Have you had this problem before? If so, do you know what caused the problem at that time? How was it treated?
  • What activity were you doing in a hot environment?
  • Do you know what the temperature, humidity level, or heat index was when you started to have symptoms?
  • What home treatment measures have you tried? Did they help?
  • What prescription and nonprescription medicines do you take?
  • Do you have any health risks?

Credits

By Healthwise Staff
William H. Blahd, Jr., MD, FACEP - Emergency Medicine
H. Michael O'Connor, MD - Emergency Medicine
Last Revised August 30, 2013

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

© 1995-2014 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

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