Fever in newborns is serious. Learn what temperature counts as a fever, which symptoms require urgent care and when to call your pediatrician for help.

Published: July 14, 2025

Estimated reading time: 3 minutes

When your baby starts to feel warm, it can be anxiety-inducing for parents. Is it “normal” or is it time to visit the emergency room? The truth is: Fever in a newborn is considered a medical emergency.

“For babies under 3 months old, a fever isn’t just a sign of illness — it can signal a serious infection that requires immediate medical attention,” said Heather M. Felton, M.D., pediatrician with Norton Children’s Medical Group. “In this case, parents should never wait to take their newborn to get emergency medical care.”

What temperature is considered a fever in newborns?

For babies under 3 months old, a fever is a rectal temperature of 100.4 F or higher. Since newborns’ immune systems are still developing, they cannot fight infections effectively. Fevers can be life-threatening if left untreated. If your newborn has a fever, do NOT wait to see if the fever goes away on its own. Seek immediate medical treatment at an emergency department.

Unlike older babies who might seem fussy or show clear signs of illness, a newborn with a fever may not always show obvious symptoms of an infection or discomfort.

How to take your baby’s temperature correctly
In babies under 3 months, a rectal temperature is considered the most accurate type of reading. If needed, you can take a temperature underneath the baby’s armpit or use a specialized temporal artery thermometer.

Other methods, such as forehead strips, ear thermometers or pacifier thermometers are not considered accurate for this age group.

When taking rectal temperature, use a specialized rectal thermometer. Always clean the thermometer before use. Never leave the newborn unattended or use force to insert the thermometer. The thermometer should be inserted no more than half an inch while your baby lies on their back or tummy. Once the temperature is ready to be read, remove and read the thermometer immediately.

When to call your pediatrician vs. seeking urgent care

“If your baby is 3 months and older, they have a fever of 101 or under, and they appear otherwise well, it’s OK to wait to be evaluated by the pediatrician the next day, if parents are comfortable,” Dr. Brockman said. “If your baby of any age has a fever and they exhibit any concerning symptoms [listed below], then you should seek emergency care.”

Go directly to an emergency department for:

• Difficulty breathing, rapid breathing or signs of distress
• Extreme fussiness or unusual lethargy
• Sudden refusal to eat or difficulty feeding
• Signs of dehydration (no wet diapers for six hours)
• Unusual skin color (paleness or rashes)
• Seizures or unusual movements

If you’re ever in doubt, or something seems “off” with your baby, never hesitate to call your Norton Children’s Medical Group pediatrician’s office; if it’s after hours, you can be transferred to the nurse triage line for any questions or guidance.