Temperature measurement

The measurement of body temperature can help detect illness. It can also monitor whether or not treatment is working. A high temperature is a fever.

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How the Test is Performed

The American Academy of Pediatrics (AAP) recommends not to use glass thermometers with mercury. The glass can break, and mercury is a poison.

Electronic thermometers are most often suggested. An easy-to-read panel shows the temperature. The probe can be placed in the mouth, rectum, or armpit.

• Mouth: Place the probe under the tongue and close the mouth. Breathe through the nose. Use the lips to hold the thermometer tightly in place. Leave the thermometer in the mouth for 3 minutes or until the device beeps.
• Rectum: This method is for infants and small children. They cannot hold a thermometer safely in their mouth. Place petroleum jelly on the bulb of a rectal thermometer. Place the child face down on a flat surface or lap. Spread the buttocks and insert the bulb end about 1/2 to 1 inch (1 to 2.5 centimeters) into the anal canal. Be careful not to insert it too far. Struggling can push the thermometer in further. Remove after 3 minutes or when the device beeps.
• Armpit: Place the thermometer in the armpit. Press the arm against the body. Wait for 5 minutes before reading or when the device beeps.

Plastic strip thermometers change color to show the temperature. This method is the least accurate.

• Place the strip on the forehead. Read it after 1 minute while the strip is in place.
• Plastic strip thermometers for the mouth are also available.

Electronic ear thermometers are common. They are easy to use. However, some users report that the results are less accurate than with probe thermometers.

Electronic forehead thermometers are more accurate than ear thermometers and their accuracy is similar to probe thermometers.

How to Prepare for the Test

Always clean the thermometer before and after using. You can use cool, soapy water or rubbing alcohol.

Wait at least 1 hour after heavy exercise or a hot bath before measuring body temperature. Wait for 20 to 30 minutes after smoking, eating, or drinking a hot or cold liquid.

Normal Results

The average normal body temperature is 98.6°F (37°C). The normal temperature can vary due to things such as:

• Age (in children over 6 months, daily temperature can vary by 1 to 2 degrees Fahrenheit)
• Differences among individuals
• Time of day (often highest in the evening)
• Which type of measurement was taken (oral, rectal, forehead, or armpit)

You need to have an accurate temperature measurement to determine if a fever is present. Be sure to tell your health care provider which type of temperature measurement you used when discussing a fever.

The exact relationship between different types of temperature measurement is unclear. However, the following general guidelines for temperature results are used:

The average normal oral temperature is 98.6°F (37°C).

• A rectal temperature is 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral temperature.
• An ear temperature is 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral temperature.
• An armpit temperature is most often 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.
• A forehead scanner is most often 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.

Other factors to take into account are:

• In general, rectal temperatures are considered to be more accurate when checking for fever in a young child.
• Plastic strip thermometers measure skin temperature, not body temperature. They are not recommended for general home use.

What Abnormal Results Mean

If the reading on the thermometer is more than 1 to 1.5 degrees Fahrenheit above your normal temperature, you have a fever. Fevers may be a sign of:

• Blood clots
• Cancer
• Certain types of arthritis, such as rheumatoid arthritis or lupus
• Diseases in the intestines, such as Crohn disease or ulcerative colitis
• Infection (both serious and non-serious)
• Many other medical problems

Body temperature can also be raised by:

• Being active
• Being in a high temperature or high humidity
• Eating
• Feeling strong emotions
• Menstruating
• Taking certain medicines
• Teething (in a young child -- but no higher than 100°F [37.7°C])
• Wearing heavy clothing

Body temperature that is too high or too low can be serious. Contact your provider if this is the case.

Related topics include:

• How to treat a fever, such as in infants
• When to call a provider for a fever

McGrath JL, Bachmann DJ. Vital signs measurement. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. 7th ed. Philadelphia, PA: Elsevier; :chap 1.

Sajadi MM, Romanovsky AA. Temperature regulation and the pathogenesis of fever. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; :chap 55.

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Ward MA, Hannemann NL. Fever: pathogenesis and treatment. In: Cherry JD, Harrison GJ, Kaplan SL, Steinbach WJ, Hotez PJ, eds. Feigin and Cherry's Textbook of Pediatric Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier; :chap 4.

Review Date 2/8/

Updated by: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

Choosing the thermometer that's best for your family can be confusing. Here's what you need to know about the most common thermometers.

Types of thermometers

In general, there are two types of thermometers. Touch, or contact, thermometers must touch the body in order to measure temperature. Remote, or no contact, thermometers can measure body temperature without touching the skin.

Contact thermometers

The most common kind of contact thermometer uses electronic heat sensors to record body temperature. These thermometers can be used on the forehead, mouth, armpit or rectum. Most electronic thermometers have a digital display that shows you the temperature reading.

Rectal temperatures provide the most-accurate readings for infants, especially those 3 months or younger, as well as children up to age 3. Temperatures taken from the armpit are usually the least accurate. For older children and adults, oral readings are usually accurate ' as long as the mouth is closed while the thermometer is in place.

The pros:

• Most electronic contact thermometers can record temperatures from the forehead, mouth, armpit or rectum ' often in less than one minute.
• An electronic contact thermometer is appropriate for newborns, infants, children and adults.

The cons:

• Parents may worry about causing discomfort when taking a child's temperature rectally.
• You need to wait 15 minutes after eating or drinking to take an oral temperature. Otherwise, the temperature of your food or drink might affect the thermometer reading.
• It can be difficult for children ' or anyone who breathes through the mouth ' to keep their mouths closed long enough to get an accurate oral reading.

If you plan to use an electronic contact thermometer to take both oral and rectal temperatures, get two thermometers and label one for oral use and one for rectal use. Don't use the same thermometer in both places.

Remote thermometers

Many schools, businesses and health care settings are screening visitors for fever. A remote thermometer that doesn't require skin contact allows people to remain further apart. Remote thermometers can be used on the forehead (temporal artery) or the ear (tympanic).

Temporal artery thermometers

Remote forehead thermometers use an infrared scanner to measure the temperature of the temporal artery in the forehead.

The pros:

• A remote temporal artery thermometer can record a person's temperature quickly and are easily tolerated.
• Remote temporal artery thermometers are appropriate for children of any age.

The cons:

• A temporal artery thermometer may be more expensive than other types of thermometers.
• This type of thermometer may be less accurate than other types. Direct sunlight, cold temperatures or a sweaty forehead can affect temperature readings. Variations on user technique, such as holding the scanner too far away from the forehead, also may affect accuracy.

Tympanic thermometers

Remote ear thermometers, also called tympanic thermometers, use an infrared ray to measure the temperature inside the ear canal.

The pros:

• When positioned properly, infrared ear thermometers are quick and generally comfortable for children and adults.
• Infrared ear thermometers are appropriate for infants older than age 6 months, older children and adults.

The cons:

• Infrared ear thermometers aren't recommended for newborns.
• Earwax or a small, curved ear canal can interfere with the accuracy of a temperature taken with an infrared ear thermometer.

Mercury thermometers

Once a staple in most medicine cabinets, mercury thermometers use mercury encased in glass to measure body temperature. Mercury thermometers are no longer recommended because they can break and allow mercury ' which is toxic ' to escape.

If you have a mercury thermometer, don't throw it in the trash. Contact your local trash collection program to see if there's a hazardous waste collection site in your area.

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