Any fever above 100.4 degrees Fahrenheit can be dangerous for a newborn. Learn how to treat baby fevers and when to visit the doctor.

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As any parent knows, there's almost nothing more frightening than your baby's first fever. It turns out that "fever phobia" is somewhat justifiable: temperatures greater than 100.4 degrees Fahrenheit can lead to life-threatening infections (such as bacterial meningitis and pneumonia) in newborns less than 3 months old. But don't panic! With the proper steps, it's unlikely that a newborn's fever will lead to complications. Here's what to do when your baby has a fever—plus new guidance from the American Academy of Pediatrics (AAP) on how to handle infant fevers.

What Causes Baby Fever?

"The most common cause of fever is infections from viruses or bacteria," such as colds, flus, ear infections, and strep throat, says Anne Tran, M.D., a pediatric hospitalist at Kaiser Permanente in Hawaii. Believe it or not, developing a fever is actually beneficial in these cases, since it proves that your baby's immune system is working properly to fight off the infection. Dr. Tran says that certain immunizations can also cause a temporary fever for as long as 48 hours, which is a normal response to vaccinations. In rare cases, fevers can point to brain disorders or autoimmune disorders.

What is Considered a Fever for a Baby?

Experts recommend using a rectal thermometer for anyone less than three years old age. These give a more accurate reading than oral thermometers, since you actually insert the bulb into the body (1/2 to 1 inch into your child's rectum). Any temperature above 100.4 degrees Fahrenheit is considered a fever, says Lana Gagin, MD, MPH, FAAP, at Spectrum Health Helen DeVos Children's Hospital. 

Besides elevated temperature, other signs of fever in babies include:

  • Fussiness
  • Excessive sleepiness
  • Lack of appetite

It's also important to make sure Baby isn't actually suffering from heat stroke, which is elevated body temperature caused by overheating. Prevent heat stroke by avoiding sun exposure, especially if your baby is less than 6 months old. "If you suspect your child is overheated, immediately move him to a cool place," says Dr. Gagin. "Call your pediatrician or take your child to the emergency room."

Baby Fever

What to Do for Baby Fever

"In newborns under three months, any temperature over 100.4 degrees is considered a medical emergency," says Dr. Tran. Babies under three months don't have fully functioning immune systems, which increases the risk of infections like bacterial meningitis and pneumonia. It's important they get evaluated right away to prevent life-threatening complications. 

If your baby is between 3 months and 6 months old, call the doctor for a fever over 101 degrees F.  You should also alert the pediatrician if your baby develops vomiting, diarrhea, ear pain, stiff neck, skin rash, inconsolable crying, shortness or breath, or other worrisome symptoms— or if they have trouble moving or waking. Also watch out for signs of dehydration in your baby, which include lack of tears and less than three or four wet diapers a day, says Dr. Tran.

Consider relieving the discomfort of a lower-grade fever with acetaminophen (for babies over 3 months) or ibuprofen (for babies over 6 months). Keep in mind, however,  that these medications temporarily mask a fever, but they won't treat symptoms. Call your doctor to discuss the proper dosage. 

Don't overdress your feverish baby or cover them in thick blankets, "as this can prevent body heat from escaping and cause their temperature to rise," says Dr. Tran. Consider giving them a lukewarm bath or dribbling a lukewarm washcloth over their body. Finally, let your child rest and keep them well hydrated. "And spend some extra time together. A hug from a loving relative goes a long way," says Dr. Gagin.

AAP Guidance on Treating Infant Fevers

So what happens if you bring your newborn to the doctor for a fever? As it turns out, there was previously no protocol for dealing with fevers in young babies; treatment could range from short observation to extensive testing at the hospital (such as a lumbar puncture). This prompted the American Academy (AAP) to release standardized guidelines— published July 2021 in Pediatrics—to set protocols for dealing with elevated temperatures in infants between 8 to 60 days old.

The new AAP guidelines are broken down by age: 8-21 days, 22-28 days, and 29-60 days. They help doctors determine whether babies with a fever (100.4 degrees Fahrenheit or more) who appear otherwise healthy should be admitted to the hospital.

"What is good about these guidelines from the perspective of a parent is they are based on all the science accumulated over the decades on how to manage an infant with a fever," Dr. Sean O'Leary, a coauthor of the guidelines, vice chair of the Committee on Infectious Diseases for the American Academy of Pediatrics, and a professor of pediatrics at the University of Colorado, Anschutz Medical Campus, told Today.

Parents should alert their pediatrician right away if their baby has a fever, especially if the baby is younger than 60 days old. Hopefully, these guidelines will eliminate unnecessary medical costs and streamline treatments in the future.