Test Overview
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?
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.
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
ovulating or having her menstrual period.
A
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.
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
antibiotics,
narcotics,
barbiturates,
antihistamines, 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
heart attack,
stroke,
heat exhaustion or
heatstroke, or burns.
- Other medical
conditions, such as arthritis,
hyperthyroidism, and even some cancers, such as
leukemia,
Hodgkin's lymphoma, and liver and
lung cancer.
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,
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 and easy to read. 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.
- Temporal artery thermometers are electronic devices that measure body temperature on the skin over an artery in the forehead (superficial temporal artery). The device has a small "cup" that is moved across the skin over the artery. Infrared energy is used to determine the temperature. When used correctly, temporal artery thermometers are accurate for measuring body temperature.1, 2
- 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, but they are not as accurate as electronic or ear thermometers. They do not contain
glass, latex, or mercury. You can reuse the thermometer during an illness and
then throw it away.
- Forehead thermometers use skin
temperature to determine body temperature. They 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 very accurate.
- 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.
How It Is Done
Before taking a body temperature,
review the instructions for how to use your thermometer. Methods of taking a
temperature are described below.
How to take an oral temperature
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
temperature.
- Place the digital or disposable thermometer
under the tongue, just to one side of the center, and close the lips tightly
around it.
- Leave the thermometer in place for the required amount
of time. Time yourself with a clock or watch. Some digital thermometers give a
series of short beeps when the reading is done.
- Remove the
thermometer and read it.
- Clean a digital thermometer with cool,
soapy water and rinse it off before putting it away.
How to take a rectal temperature
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
essential.
- Apply a lubricant jelly or petroleum jelly,
such as Vaseline, on the bulb of the thermometer so that you can insert it
easily.
- When measuring the temperature of babies or small children,
turn the child face down on your lap or on a flat covered or padded surface,
such as a bed. Choose a quiet place so that the child won't be distracted or
move around too much.
- Spread the child's buttocks with one hand and
gently insert the bulb end of the rectal thermometer about
0.5 in. (1.25 cm) to
1 in. (2.5 cm) into the anal
canal with your other hand. Don't force it into the rectum. Hold the
thermometer in place with two fingers close to the anal opening (not near the
end of the thermometer). Pressing the child's buttocks together will help keep
the thermometer in place.
- Leave the thermometer in place for the
required amount of time. Some digital thermometers give a series of short beeps
when the reading is done. Time yourself with a watch or clock.
- Remove the thermometer and read it.
- Clean a digital thermometer with cool, soapy water and
rinse it off before putting it away.
- Do not use a thermometer to
take an oral temperature after it has been used to take a rectal
temperature.
See a picture of
how to take the rectal temperature of a baby.
How to take an armpit (axillary) temperature
Taking a temperature in the armpit may not be as accurate as
taking an oral or rectal temperature.
- Place the thermometer under the arm with
the bulb in the center of the armpit.
- Press the arm against the
body and leave the thermometer in place for the required amount of time. Time
yourself with a watch or clock.
- Remove the thermometer and read it.
An armpit temperature reading may be as much as 1°F (0.6°C) lower than an oral
temperature reading.
- Clean a digital thermometer with cool, soapy
water and rinse it off before putting it away.
How to take an ear (tympanic) temperature
Ear thermometers
may need to be cleaned and prepared for use. These steps can be followed when
using an ear thermometer, but be sure to follow the instructions for your specific
model.
- Check that the probe is clean and free of
debris. If dirty, wipe it gently with a clean cloth. Do not immerse the
thermometer in water.
- To keep the probe clean, a disposable probe
cover should be used. Use a new probe cover each time you take an ear
temperature. Attach the disposable cover to the probe.
- Turn the
thermometer on.
- For babies younger than 12 months, pull the earlobe
down and back. This will help place the probe in the ear canal. Center the
probe tip in the ear and push gently inward toward the eardrum.
- For
children older than 12 months and for adults, pull the earlobe up and back.
Center the probe tip in the ear and push gently inward toward the
eardrum.
- Press the "on" button to display the temperature
reading.
- Remove the thermometer and throw away the used probe
cover.
How to take a temporal artery temperature
- Remove the cap over the cup part of the thermometer, if it has a cap.
- Turn on the thermometer.
- Place the thermometer cup on the skin in the center of the forehead. Make sure nothing is between the thermometer cup and the skin.
- Press the button for making a measurement.
- Slide the thermometer across the forehead to one side (not up or down).
- Listen for a sound from the device. Most temporal artery thermometers have a signal (such as a beep or other sound) that means the measurement is ready to read.
- Remove the thermometer from the forehead, and read the temperature.
How to take a forehead temperature
- Press the entire plastic
strip firmly against a dry forehead.
- Hold the thermometer in place
for the required amount of time. Time yourself with a watch or
clock.
- Read the temperature before removing the
thermometer.
- Clean the thermometer with cool soapy water and rinse
it off before putting it away.
- Forehead thermometers are not as
accurate as electronic and ear thermometers. If your baby is younger than age 3
months or your child's fever rises higher than
102°F (39°C), recheck the
temperature using a better method.
How to use a pacifier thermometer
- Put together all of the pieces of the pacifier if you need to.
Some pacifier thermometers can be used as regular pacifiers and need to have
the temperature part attached.
- Let your child suck on the nipple
for the required amount of time. Time yourself with a watch or
clock.
- Remove the pacifier and read the
temperature.
- Clean the pacifier with cool, soapy water and rinse it
off before putting it away.
- Pacifier thermometers are not as
accurate as electronic and ear thermometers. If your baby is younger than age 3
months or your child's fever rises higher than
102°F (39°C), recheck the
temperature using a better method.
How It Feels
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.
Taking your
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
thermometers.
Taking your temperature with a plastic strip
thermometer feels like having an adhesive bandage on your forehead. Although it
causes very little discomfort, it is not as reliable as other methods, so
another kind of thermometer should be used if the plastic strip shows an
abnormal temperature.
Risks
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.
Results
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.
Body temperature| Normal: | 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
ovulation. |
|---|
|
Abnormal: | Oral, ear (tympanic), rectal, or temporal artery temperature - Fever: 100.4°F (38°C) to 103.9°F (39.9°C)
- High fever: 104°F (40°C) and higher
|
|---|
Armpit (axillary) temperature - Fever: 99.4°F (37.4°C) to 102.9°F (39.4°C)
- High fever: 103°F (39.5°C) and higher
|
A rectal or ear temperature of
less than 97°F (36.1°C)
means a low body temperature (hypothermia). |
What Affects the Test
Inaccurate temperature readings
can be caused by:
- Not keeping your mouth closed around the
thermometer when taking an oral temperature.
- Not leaving a
thermometer in place long enough before reading it.
- Not putting the
proper thermometer in the right place.
- Not following the
instructions for proper use that come with the thermometer.
- A weak
or dead thermometer battery.
- Taking an oral temperature within 20
minutes after smoking or drinking a hot or cold liquid.
- Taking a
temperature by any method within an hour of exercising vigorously or taking a
hot bath.
What To Think About
- Thermometers with a digital display usually
need a battery. If your thermometer uses a battery, make sure it is working
before taking a temperature.
- Body temperature is only one way of
monitoring your health. Besides temperature, other basic measurements to
monitor your health include your pulse, breathing rate (respiration), and blood
pressure. These basic measurements are called your vital signs.
- A
fever can make you feel uncomfortable. To treat the discomfort of a fever, wear
light clothing and use light blankets or other bedding. Drink cool liquids. A
bath or shower with lukewarm (not cool) water can lower body temperature. Cool
or cold water can cause shivering and can cause the blood vessels near the skin
to contract, which will raise the body temperature
further.
- Fever-reducing medicines can lower body temperature and help you feel more comfortable. When a fever
causes discomfort, use over-the-counter acetaminophen or a nonsteroidal anti-inflammatory medicine (NSAID), such as ibuprofen. Read and follow all instructions on the label. Aspirin also reduces fever but should not be given to anyone
younger than age 20 because of the risk of
Reye syndrome.
Talk to your doctor before you give fever medicine to a baby who is 3 months of age or younger. This is to make sure a young baby's fever is not a sign of a serious illness. For more information about reducing fever, see the topics Fever, Age 11 and Younger and Fever, Age 12 and Older.
- 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.
References
Citations
- 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.
Credits
| By | Healthwise Staff |
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| Primary Medical Reviewer | Susan C. Kim, MD - Pediatrics |
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| Specialist Medical Reviewer | Thomas Emmett Francoeur, MD, MDCM, CSPQ, FRCPC - Pediatrics |
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| Last Revised | November 13, 2012 |
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