Body Temperature

What is body temperature?

Body temperature is a measure of the body's ability to generate and get rid of heat. The body is very good at keeping its temperature within a narrow, safe range in spite of large variations in temperatures outside the body.

When you are too hot, the blood vessels in your skin expand (dilate) to carry the excess heat to your skin's surface. You may begin to sweat, and as the sweat evaporates, it helps cool your body. When you are too cold, your blood vessels narrow (contract) so that blood flow to your skin is reduced to conserve body heat. You may start shivering, which is an involuntary, rapid contraction of the muscles. This extra muscle activity helps generate more heat. Under normal conditions, this keeps your body temperature within a narrow, safe range.

Where is body temperature measured?

Your body temperature can be measured in many locations on your body. The mouth, ear, armpit, and rectum are the most commonly used places. Temperature can also be measured on your forehead.

What are Fahrenheit and Celsius?

Reference Thermometers Opens New Window Reference Opens New Window are calibrated in either degrees Fahrenheit (°F) or degrees Celsius (°C), depending on the custom of the region. Temperatures in the United States are often measured in degrees Fahrenheit, but the standard in most other countries is degrees Celsius.

What is normal body temperature?

Most people think of a "normal" body temperature as an oral temperature of 98.6°F (37°C). This is an average of normal body temperatures. Your temperature may actually be 1°F (0.6°C) or more above or below 98.6°F (37°C). Also, your normal body temperature changes by as much as 1°F (0.6°C) throughout the day, depending on how active you are and the time of day. Body temperature is very sensitive to hormone levels and may be higher or lower when a woman is Reference ovulating Opens New Window or having her menstrual period.

A Reference rectal Opens New Window or ear (tympanic membrane) temperature reading is slightly higher than an oral temperature reading. A temperature taken in the armpit is slightly lower than an oral temperature reading. The most accurate way to measure body temperature is to take a rectal temperature.

What is a fever?

In most adults, an oral temperature above 100°F (37.8°C) or a rectal or ear temperature above 101°F (38.3°C) is considered a fever. A child has a fever when his or her rectal temperature is 100.4°F (38°C) or higher.

What can cause a fever?

A fever may occur as a reaction to:

• Infection. This is the most common cause of a fever. Infections may affect the whole body or a specific body part (localized infection).
• Medicines, such as Reference antibiotics Opens New Window, Reference narcotics Opens New Window, Reference barbiturates Opens New Window, Reference antihistamines Opens New Window, and many others. These are called drug fevers. Some medicines, such as antibiotics, raise the body temperature directly; others interfere with the body's ability to readjust its temperature when other factors cause the temperature to rise.
• Severe trauma or injury, such as a Reference heart attack Opens New Window, Reference stroke Opens New Window, Reference heat exhaustion Opens New Window or Reference heatstroke Opens New Window, or burns.
• Other medical conditions, such as arthritis, Reference hyperthyroidism Opens New Window, and even some cancers, such as Reference leukemia Opens New Window, Reference Hodgkin's lymphoma Opens New Window, and liver and Reference lung cancer Opens New Window.

Can a low body temperature be dangerous?

An abnormally low body temperature (hypothermia) can be serious, even life-threatening. Low body temperature may occur from cold exposure, Reference shock Opens New Window, alcohol or drug use, or certain metabolic disorders, such as Reference diabetes Opens New Window or Reference hypothyroidism Opens New Window. 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 Reference 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.

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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 Reference Terms of Use. Reference How this information was developed to help you make better health decisions.