From November 2009 AAP News (copyright 2009, American Academy of Pediatrics, may be freely copied and distributed with proper attribution; author is Alyson Sulaski Wyckoff); see end for additional thoughts not included in this AAP article:

AAP News Parent Plus:  Information from Your Pediatrician

Thermometer use 101

If your child feels warm, looks flushed, is sweating or shivering, or has flu symptoms, you might suspect fever.  Using a thermometer is the only sure way to know if a fever is present.

A basic digital version may be the most practial and reliable way to determine if your child has a fever.  Mercury thermometers should not be in your medicine cabinet; the silver liquid inside is dangerous if the thermometer breaks.

Use a digital thermometer to take a rectal (in the bottom), oral (in the mouth) or axillary (under the arm) temperature.  A tympanic (ear) thermometer, which is more expensive, is another option.  Other methods are available but are not recommended by the American Academy of Pediatrics (AAP) at this time.

Temperatures taken rectally or orally are more accurate than those obtained using the axillary or tympanic methods.  If your child is younger than 3 years old, a rectal temperature gives the best reading.  At around 4 or 5, you can feel comfortable taking a temperature by mouth.

A normal temperature for a child may range from 97 degrees Fahrenheit (F) to 100.4 degrees F.  In general, the AAP considers anything over 100.4 degrees F to be a possible fever.

Taking a rectal temperature:

• Clean the end of the thermometer with rubbing alcohol or soap and water; rinse in lukewarm water and dry.  Apply a small amount of lubricant, such as petroleum jelly, on the end.
• Place your child tummy down across your lap.  Hold the child by placing your palm against his lower back.  Or, place the child face up and bend his legs to the chest.  Rest your free hand against the back of thighs.
• With the other hand, turn the thermometer on, and insert it 1/2 to 1 inch into the anal opening (not too far).  Hold the thermometer in place loosely with two fingers, keeping your hand cupped around your child's bottom.  In about a minute, when you hear the beep, remove it and check the reading.
• Re-clean.  Be sure the thermometer is labeled so it's not accidentally used in the mouth.

Taking an oral temperature:

• Wait 15 minutes after the child has been eating or drinking before taking a temperature.
• Clean thermometer.  Turn the thermometer on, and place the tip under the tongue toward the back of the child's mouth.  Hold in place for a minute until you hear a beep.

Taking an axillary temperature:

• Turn on the thermometer, and place the small end in your child's armpit (thermometer should touch skin, not clothing).
• Gently hold the arm in place until the thermometer beeps.

Taking a tympanic temperature:

The AAP advises against using this method for infants younger than 3 months.  While a tympanic thermometer provides speedy results, the device needs to be inserted at the right angle in a child's ear to provide an accurate reading.  Don't use these devices right after a child has been swimming or bathing or if ear pain is present.

Types of digital thermometers for use by age and technique/type

Newborn to 3 months:  Rectal (in the bottom)

3 months-3 years:  Rectal, axillary (under arm), tympanic (ear)

4-5 years:  Rectal, oral (in the mouth), axillary, tympanic

5 years and older:  Oral, axillary, tympanic

Additional input from Virginia Pediatric & Adolescent Center:

We consider 100.4 or higher a fever (and a reason to call us immediately, day or night) in children under 3 months old.  If your child is 3 months or older, most physicians in our group use a definition of 101 or higher as a "true fever." Teething should not cause a fever of 101 or higher.  Unless a child has known allergies or other contraindications, acetaminophen (Tylenol) can be used in children of any age, and ibuprofen (Motrin or Advil) can be used in children age 6 months and older for a child with a fever. 

If your child is 3 months or older and has clear upper respiratory symptoms (runny nose and cough) and is drinking well and is not struggling to breathe, there may be a fever the first 2-3 days of a cold.  Please call or come to walk-in clinic if your child has persistent fevers of 3 days or more with a cold, a fever whose onset does not correspond to the onset of cold symptoms (such as starting a fever after several days of cold symptoms), fevers without an obvious cause, lethargy (it is normal for children to be a bit tired with a fever, but your child should still be responding to you appropriately), poor fluid intake, urine output fewer than 4 times in a 24-hour period, no tears when crying (a sign of dehydration), pain or ear-tugging or inconsolable crying, a stiff neck or eye sensitivity to light, purple skin spots, asthma or wheezing along with cold symptoms, or any other concerning symptoms.