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, and cause 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 difficult 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. Caffeine or alcohol also increase your risk for 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.
- Summer heat waves. People who live in cities are especially vulnerable to illness during a summer 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.
Use the Check Your Symptoms section to decide if and when you should see a doctor.
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.
- 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 often, 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 child has stopped breathing, begin rescue breathing.
- Do not give aspirin or acetaminophen to reduce a high body temperature that can occur with heatstroke. These 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. Drinks such as sports drinks that contain electrolytes work best. 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.
Heat syncope (fainting) usually does not last long and improves once 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
Use the Check Your Symptoms section to evaluate your symptoms if any of the following occur during home treatment:
- A seizure occurs.
- Decreased mental alertness develops.
- Shortness of breath develops.
- You are unable to lower the body temperature.
- Vomiting occurs.
- Symptoms become more severe or frequent.
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. Drinks, such as sports drinks, that have
electrolytes work best.
- Drink on schedule. Two hours before exercising, drink 24 fl oz (710 mL) of fluid. Drink 16 fl oz (473 mL) of fluid 15 minutes before exercising. Continue drinking 8 fl oz (237 mL) of fluid every 15 minutes while exercising.
- Drink rehydration drinks or sports drinks which are absorbed 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 to 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 while standing. This prevents blood from pooling in your lower legs, which can lead to fainting. Wear support hose to stimulate circulation while standing for long periods of time to prevent swelling (heat edema).
- 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 once 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?
|Author||Jan Nissl, RN, BS|
|Editor||Susan Van Houten, RN, BSN, MBA|
|Associate Editor||Tracy Landauer|
|Primary Medical Reviewer||H. Michael O'Connor, MD - Emergency Medicine|
|Primary Medical Reviewer||William M. Green, MD - Emergency Medicine|
|Specialist Medical Reviewer||Kathleen Romito, MD - Family Medicine|
|Last Updated||October 7, 2008|