An abnormal body temperature can signal a potentially serious problem in an infant (birth to 1 year). Both a low or a high body temperature can be problematic for a baby, often indicating an underlying infection. All parents and other infant caregivers need to know the best ways take a baby's temperature and when to seek medical care for an abnormal body temperature.
Normal Temperature Ranges
The normal range for body temperature in infants (and older children) varies, depending on the type of thermometer used. The American Academy of Pediatrics (AAP) recommends use of a digital rectal (in the baby's bottom) thermometer for infants from birth to 3 months old. For infants 3 to 12 months old, recommended options include a digital rectal, axillary (armpit) or tympanic (ear) temperature measurement. The normal body temperature ranges using these devices are:
- Rectal: 97.9 F to 100.4 F (36.6 C to 38.0 C)
- Axillary: 97.8 F to 99.5 F (36.5 C to 37.5 C)
- Tympanic: 96.4 F to 100.4 F (35.8 C to 38.0 C)
The AAP warns that glass mercury thermometers should never be used because of the risk of breakage and exposure to toxic mercury. Other types of thermometers -- such as pacifier thermometers and temporal artery (forehead) thermometers -- are not currently recommended by the AAP.
Rectal temperature using a digital thermometer is the most accurate way to check your baby's body temperature. If you get an abnormal axillary or tympanic result, you may want to recheck your baby's temperature rectally.
Abnormal Infant Body Temperature
Any body temperature outside of the ranges noted is considered abnormal. An elevated temperature indicates a fever, which is often due to a bacterial or viral infection. Overheating is another relatively common cause of fever in babies. Infants are more susceptible to overheating because their capacity for sweating is not as developed as it is in older children and adults. This can be compounded by over dressing your baby or bundling your little one up with too many blankets -- common rookie mistakes among new parents.
A low body temperature can also indicate an infection in a baby, especially during the first few months of life. A cool environment is also a relatively common cause of a slightly decreased temperature because babies lose body heat more rapidly than older children or adults. As a rule of thumb, a baby requires one more layer of clothing than you are comfortable wearing. For example, if you are comfortable in a long-sleeved shirt and pants, your baby will need similar clothing plus a light blanket or a sweater.
When to Call Your Doctor
The AAP recommends you call your doctor right away in these circumstances for infants:
- Your baby is 3 months old or younger and has an abnormal body temperature, even if the infant doesn't seem sick
- Your baby is 3 to 12 months and spikes a fever of 104 F or higher
- Your baby has a fever and has been in very hot conditions
- Your baby has an abnormal body temperature and other symptoms, such as vomiting, diarrhea, a rash, or is very fussy or unusually sleepy
- Your baby has a fever for more than 24 hours
- Your baby has a seizure
If any of these circumstances occur and you cannot reach your doctor right away, take your baby to the nearest urgent or emergency care facility. Do not give your baby any fever-lowering medicine until you've been seen by a healthcare provider. Never give your baby aspirin, which increases the risk for a potentially life-threatening condition called Reye syndrome.
Reviewed and revised by: Tina M. St. John, M.D.