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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.
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.
Thermometers 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.
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
ovulating or having her menstrual period.
rectal 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.
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
A fever may occur as a
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
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
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 who have chronic health problems have the
greatest risk of this type of 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
Body temperature is checked to:
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
Several different types of thermometers are
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.
Before taking a body temperature,
review the instructions for how to use your specific thermometer. General methods of taking a
temperature are described below.
Oral is the most
common method of taking a temperature. To get an accurate temperature, the
person must be able to breathe through the nose. If this is impossible because
of a stuffy nose or lack of cooperation, use the rectum, ear, or armpit to take the
This is the
location to measure body temperature most accurately. It is recommended for
babies, small children, and people who cannot hold a thermometer safely in
their mouths. It is also used when getting the most accurate measurement is
See a picture of
how to take the rectal temperature of a baby.
Taking a temperature in the armpit may not be as accurate as
taking an oral or rectal temperature.
may need to be cleaned before they are used.
Taking your temperature by mouth is only mildly uncomfortable,
since you must keep your mouth closed and breathe through your nose while the
thermometer is in place.
Taking a rectal temperature can be
slightly uncomfortable but should not be painful.
temperature with an ear thermometer causes little or no discomfort. It is not
inserted very far into the ear, and it provides a reading in only a few
seconds. For this reason, the ear thermometer is widely used in doctor offices and hospitals. But it may be less accurate than rectal
Taking your temperature with a thermometer that is placed on the skin, such as a plastic strip
thermometer or a temporal artery thermometer , should not cause any discomfort. Use of a plastic strip thermometer feels like having an adhesive bandage on your forehead. The slight pressure of a temporal artery thermometer as it glides across the skin is not painful.
There is very little risk of complications from
taking a temperature.
When taking a rectal temperature, do not
insert the thermometer into the rectum more than
0.5 in. (1.25 cm) to
1 in. (2.5 cm). Further
insertion can be painful and may damage rectal tissues.
Body temperature is a measure of the
body's ability to generate and get rid of heat.
When you tell your doctor about your temperature
measurement, be sure to mention whether it was taken on the forehead or in the
mouth, rectum, armpit, or ear.
The average normal temperature
is 98.6°F (37°C). But "normal"
varies from person to person. Your temperature will also vary throughout the
day, usually being lowest in the early morning and rising as much as 1°F
(0.6°C) in the early evening. Your temperature may also rise by 1°F (0.6°C) or
more if you exercise on a hot day. A woman's body temperature typically varies
by 1°F (0.6°C) or more through her
menstrual cycle, peaking around the time of
Oral, ear (tympanic), rectal, or temporal artery temperature
Armpit (axillary) temperature
A rectal or ear temperature of
less than 97°F (36.1°C)
means a low body temperature (hypothermia).
Inaccurate temperature readings
can be caused by:
Al-Mukhaizeem F, et al. (2004). Comparison of temporal artery, rectal and esophageal core temperatures in children: Results of a pilot study. Paediatrics and Child Health, 9(7): 461–465.
Greenes DS, Fleisher GR (2001). Accuracy of a noninvasive temporal artery thermometer for use in infants. Archives of Pediatrics and Adolescent Medicine, 155(3): 376–381.
Other Works Consulted
Auwaerter PG (2007). Approach to the patient with fever. In LR Barker et al., eds., Principles of Ambulatory Medicine, 7th ed., pp. 457–465. Philadelphia: Lippincott Williams and Wilkins.
El-Radhi AS, Barry W (2006). Thermometry in paediatric practice. Archives of Disease in Childhood, 91(4): 351–356.
January 18, 2013
Susan C. Kim, MD - Pediatrics & John Pope, MD - Pediatrics
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