An abnormally low body temperature (hypothermia) can be serious, even life-threatening. Low body temperature may occur from cold exposure, shock, alcohol or drug use, or certain metabolic disorders, such as diabetes or hypothyroidism. A low body temperature may also be present with an infection, particularly in newborns, older adults, or people who are frail. An overwhelming infection, such as sepsis, may also cause an abnormally low body temperature.

Can a high body temperature be dangerous?

Heatstroke occurs when the body fails to regulate its own temperature, and body temperature continues to rise. Symptoms of heatstroke include mental changes (such as confusion, delirium, or unconsciousness) and skin that is red, hot, and dry, even under the armpits.

Classic heatstroke can develop without exertion when a person is exposed to a hot environment and the body is unable to cool itself effectively. In this type of heatstroke, the body's ability to sweat and transfer the heat to the environment is reduced. A person with heatstroke may stop sweating. Classic heatstroke may develop over several days. Babies, older adults, and people with chronic health problems have the greatest risk of this type of heatstroke.

Exertional heatstroke may develop when a person is working or exercising in a hot environment. A person with heatstroke from exertion may sweat profusely, but the body still produces more heat than it can lose. This causes the body's temperature to rise to high levels.

Both types of heatstroke cause severe dehydration and can cause body organs to stop functioning. Heatstroke is a life-threatening medical emergency, requiring emergency medical treatment.

Why It Is Done

Body temperature is checked to:

• Detect fever.
• Detect abnormally low body temperature (hypothermia) in people who have been exposed to cold.
• Detect abnormally high body temperature ( hyperthermia) in people who have been exposed to heat.
• Help monitor the effectiveness of a fever-reducing medicine.
• Help plan for pregnancy by determining if a woman is ovulating.

How To Prepare

Take your temperature several times when you are feeling well to find out what is normal for you. Check your temperature in both the morning and evening, since body temperature can vary by as much as 1°F (0.6°C) throughout the day.

Wait at least 20 to 30 minutes after smoking, eating, or drinking a hot or cold liquid before taking your temperature. Also wait at least an hour after vigorous exercise or a hot bath.

Several different types of thermometers are available:

• Electronic thermometers are plastic and shaped like a pencil, with a display window at one end and the temperature probe at the other end. They work by measuring how well electricity travels through a wire. Electronic thermometers are used in the mouth, rectum, or armpit. They are easy to use, easy to read, and are accurate. If you buy an electronic thermometer, check the package for information about its accuracy. See a picture of an electronic thermometer .
• Ear thermometers are plastic and come in different shapes. They use infrared energy to measure body temperature. The small cone-shaped end of the thermometer is placed in the ear, and body temperature shown on a digital display. The results appear within seconds. Some models also show the corresponding oral and rectal readings. See a picture of an ear thermometer .
• Forehead thermometers use skin temperature to determine body temperature. Some have a soft disc that are pressed against the forehead and show the temperature on a digital display. Other types are thin pieces of plastic with numbers on them. You press the strip against a person’s forehead, and the temperature makes some numbers change colors or light up. These thermometers are not as accurate as electronic and ear thermometers.
• Disposable thermometers are thin flat pieces of plastic with colored dots and temperature markings on one end. The color of the dots shows the temperature. Disposable thermometers can be used in the mouth or rectum. A patch form can be used on a baby's skin to measure temperature continuously for 48 hours. These thermometers are safe and accurate within 0.2°F (0.1°C). They do not contain glass, latex, or mercury. You can reuse the thermometer during an illness and then throw it away.
• Pacifier thermometers are shaped like a baby’s pacifier but have a display that shows the temperature. You place the pacifier in your child’s mouth to measure temperature. These thermometers may take longer to get a reading and are not as accurate as other types.

Glass thermometers containing mercury are no longer recommended. If you have a glass thermometer, contact your local health department for instructions on how to dispose of it safely. If you break a glass thermometer, call your local poison control center immediately.