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Your Baby's Temperature and Fever

Reviewed by Renee A. Alli, MD on May 31, 2021
Mother checking temperature of baby

During the first few months of your baby’s life, pay special attention if you think they have a fever. Their immune system isn’t as good at fighting infections as it will be at 3 or 4 months of age.

When Is It a Fever?

Most doctors say a baby has a fever if their temperature rises to 100.4 F or above. It’s best to take their temperature rectally. Take a few readings when your infant is well to get a sense of what their normal temperature is.

When to See a Doctor

If your baby is under age 3 months and has a fever, take them to a doctor. For at least the first 6 months of life, call your doctor anytime they have a fever.

At your baby’s next checkup you can ask if the doctor has a “fever policy.” That will give you a better idea about when you need to call. If you’re worried, take the better-safe-than-sorry approach: Dial them up.

Fever is only part of the story. Sometimes a baby can be sick even if they don’t have a fever. A more important question is: Does your newborn show other symptoms of illness? Call the doctor if your baby:

  • Is irritable
  • Is inactive
  • Is sluggish
  • Doesn't eat
  • Has trouble breathing
  • Has a rash
  • Vomits
  • Has diarrhea

What Causes Fever?

Your baby could have a fever for many reasons, but the most likely is infection. Simple things such as colds can cause a fever, but so can very serious infections such as meningitis. If your baby is under 3 months and has a fever, see a doctor.

Show Sources

SOURCE: 

Behrman, R., Kliegman, R., and Jenson, H. Nelson Textbook of Pediatrics, 17th edition, Saunders, 2004.

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