Fever

Medical Author: John P. Cunha, DO, FACOEP
Medical Editor: Melissa Conrad Stöppler, MD

• What is a fever?
• How should I take a temperature for fever?
• Measuring an axillary (under the armpit) temperature for fever
• Measuring fever by eardrum temperature
• Measuring fever by oral temperature
• Measuring fever by rectal temperature
• Measuring fever by electronic thermometer
• How is fever treated?
• When should I seek medical care for a fever?
• Aches, Pain, Fever At A Glance

What is a fever?

Fever refers to an elevation in body temperature. Technically, any body temperature above the normal oral measurement of 98.6 F (37 C) or the normal rectal temperature of 99 F (37.2 C) is considered to be elevated. However, these are averages, and your normal temperature may actually be 1 F (0.6 C) or more above or below the average of 98.6 F. Body temperature can also vary up to 1 F (0.6 C) throughout the day.

Thus, fever is not considered medically significant until body temperature is above 100.4 F (38 C). Fever serves as one of the body's natural defenses against bacteria and viruses which cannot live at a higher temperature. For that reason, low fevers should normally go untreated, unless accompanied by troubling symptoms.

Also, the body's defense mechanisms seem to work more efficiently at a higher temperature. Fever is just one part of an illness, many times no more important than the presence of other symptoms such as cough, sore throat, etc.

Fevers of 104 F (40 C) or higher demand immediate home treatment and subsequent medical attention, as they can result in delirium and convulsions, particularly in children.

How should I take a temperature for fever?

Digital thermometers can be used to measure rectal, oral, or axillary (under the armpit) temperatures. The American Academy of Pediatrics does not recommend use of mercury thermometers (glass), and they encourage parents to remove mercury thermometers from their households to prevent accidental exposure to this toxin.

Measuring an axillary (under the armpit) temperature for fever:

Axillary temperatures are not as accurate as rectal or oral measurements, and these generally measure one degree lower than a simultaneously obtained oral temperature.

• Place the tip of the digital thermometer in your child's armpit.



• Leave in place about one minute or until you hear a beep to check a digital reading.

Measuring fever by eardrum temperature:

Tympanic (ear) thermometers must be placed correctly in your child's ear to be accurate. Too much earwax can cause the reading to be incorrect.

Eardrum temperature measurements are not accurate in small children and should not be used in children under 3 years (36 months) of age. This is especially true in infants below 3 months of age when obtaining an accurate temperature is very important.

Measuring fever by oral temperature:

Children 4 to 5 years old and adults can have their temperature taken with a digital thermometer under the tongue with their mouth closed.

• Clean the thermometer with soapy water or rubbing alcohol and rinse.



• Turn the thermometer on and place the tip of the thermometer as far back under the tongue as possible.



• The thermometer should remain in place for about one minute or until you hear the beep. Check the digital reading.

Avoid hot or cold drinks within 15 minutes of oral temperature measurement to ensure correct readings.

Measuring fever by rectal temperature:

The American Academy of Pediatrics recommends rectal temperature measurements for children under 3 years, as this gives the most accurate reading of core temperature.

• Clean the thermometer with soapy water or rubbing alcohol and rinse with cool water.



• Use a small amount of lubricant, such as petroleum jelly, on the end.



• Place the child prone (belly-side down) on a firm surface, or place your child face up and bend his legs to his chest.



• After separating the buttocks, insert the thermometer approximately ½ to 1 inch into the rectum. Do not inset it too far.



• Hold the thermometer in place, loosely keeping your hand cupped around your child's bottom, and keep your fingers on the thermometer to avoid it accidently sliding further into the rectum. Keep it there for about one minute, until you hear the beep.



• Remove the thermometer, and check the digital reading.



• Label the rectal thermometer so it's not accidentally used in the mouth.

A rectal temperature will read approximately one degree higher than a simultaneously obtained oral temperature.

Next: How is fever treated? »