Updated on May 28th, 2023 // by Katie Griffin
Estimated reading time: 5 minutes
Even the most experienced parents worry when their new baby seems to have a temperature. So, what is considered a fever for a baby? Let’s learn all about infant fevers and what to do if you think your baby has one.
Table of contents
What is considered a fever for a baby?
A fever is the normal response that your baby’s body has to fighting infection. A fever will usually go away within 72 hours. While mild fevers are typically not concerning, fevers are considered more serious in babies who are 3 months and younger.
If your baby is 3 months and younger, The American Academy of Pediatrics suggests that parents call their pediatrician if baby has a rectal temperature of 100.4°F/38.0°C or higher (1).
Why might my baby have a fever?
A fever is often a symptom that your baby’s immune system is fighting off an illness. This can include a cold or an ear infection. Although less common, more serious infections such as pneumonia, meningitis, or an infection in baby’s blood from maternal Group B Streptococcus (GBS) can also cause a fever.
Another reason baby might have a fever is if he’s over-bundled or dressed too warmly. My husband and I had this happen once to our first baby when we put her to sleep for a nap wrapped in a polar fleece blanket. She woke up fevering and sweaty, and even threw up 🙁 . Fortunately she was fine afterwards, but it was a pretty awful lesson to learn. Infants have a hard time regulating their own temperatures, so they’re more prone to overheating. Since overheating is also a risk for SIDS (2), it’s best to skip heavy blankets and instead opt for light weight clothing and a light weight sleep sack.
What are symptoms that my baby may have a fever?
Common symptoms that your baby might have a fever include:
- Warm head or belly
- Fussier than usual
- Poor sleeping
- Poor eating
- Less active or lethargic
- Convulsions or seizures
How do I check my baby’s temperature?
There are a few different options to check your baby’s temperature for a fever. The most common methods are rectally, under the arm (axillary), or through the tympanic membrane (ear).
- The first choice for an infant is a rectal temperature. This provides the most accurate reading because it reflects baby’s core temperature, which is normally anywhere between 97.7°F and 99.7°F (3). It must be done with caution, though, because there’s a risk of causing a tear in the mucosa of the rectum.
- Placing a thermometer in baby’s armpit is a safer, easier option, although it is less accurate than a rectal reading. Skin temperature is slightly lower than core body temperature. Thus, an axillary temperature will generally come in lower than a rectal temperature.
- The easiest method of all is to use a tympanic membrane thermometer in baby’s ear. Unfortunately, these are NOT recommended for use in babies under 3 months old. Their ear canal is too small to insert the thermometer probe, and it will yield inaccurate readings.
When considering all 3 options, we know that most children don’t like to have their temperature taken rectally. If this is the case with your baby, you can first take her temperature under her armpit or ear (if she’s old enough) to help you know generally whether or not she has a fever. If so, follow up by also taking a rectal temperature for a more exact reading.
Tips for taking a rectal temperature:
Follow these simple tips to safely take your baby’s rectal temperature (4):
- If you’re using a glass thermometer, be sure it’s meant for rectal and not oral use. A rectal thermometer has a fatter bulb than an oral one does.
- Clean the thermometer with cool, soapy water and then rinse
- Cover the tip of the thermometer with petroleum jelly
- Place baby on his back with knees bent
- Gently insert the thermometer tip in the rectum about 3/4 – 1 inch while holding it firmly with your fingers
- If using a glass thermometer, remove the thermometer after about 2 minutes and read the temperature. An electric thermometer gives a much faster reading, and will beep when finished
- Clean the thermometer
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(1) American Academy of Pediatrics. (2010). Bright Futures parent Handout: 2 to 5 Day Visit. Retrieved from brightfutures org.
(2) American Academy of Pediatrics (2016). SIDS and Other Sleep-Related Infant Deaths: Updated 2016 Recommendations for a Safe Infant Sleeping Environment. Pediatrics, Volume 138, number 5.
(3) Hockenberry, M., Wilson, D. (2008). Wongs Nursing Care of Infants and Children. Elsevier, St. Louis, MO. pg 242
(4) How to take a child’s temperature. (2000). Paediatrics & Child Health, 5(5), 277–278.