Newborn Fever: What to Do If Your Baby Has a Fever

You’ve just taken your baby’s temperature—maybe because they felt a little warm, seemed fussier than usual, or something just felt off. Then you see the number: 100.8°F. Your heart skips a beat.

If your baby is under 2 months old, you might be wondering: Is this a big deal? Should I call the doctor? Am I overreacting?

You're not alone—and you're absolutely right to pause and ask those questions. Fevers in newborns are one of the few times when we don’t wait and see. In this post, we’ll break down exactly what a fever means in a baby under 60 days, what the current pediatric guidelines recommend, and how to handle it calmly and confidently.

When to Worry About Fever in a Newborn

If your baby is under 2 months old and has a rectal temperature of 100.4°F (38°C) or higher, it’s considered a fever—and that’s always worth a call to your pediatrician or a trip to the ER.

Even if your little one seems totally fine, fevers in this age group can be the first (and sometimes only) sign of an infection. It’s not meant to scare you—it’s just something we take seriously because newborn immune systems aren’t quite ready to fight off germs the way older babies can.

What Is Considered a Fever in a Baby?

A rectal temperature of 100.4°F (38°C) or more is officially a fever in a baby under 60 days.
*** Tip: Always use a rectal thermometer for the most accurate reading in this age group.

What Causes Fever in Young Infants?

Common causes can include:

• Viral infections (like colds or RSV)

• Urinary tract infections

• Bacterial infections in the blood or spinal fluid (though rare, these are what doctors are screening for)

When to Go to the ER for a Baby’s Fever

Here’s what usually happens based on baby’s age:

If Your Baby Is 0–28 Days Old:

• Your doctor or ER team will likely recommend:

  • Blood and urine tests

  • A spinal tap (to check for meningitis)

  • Hospital admission and antibiotics, even if baby looks fine

• This is the safest approach while results come back

If Your Baby Is 29–60 Days Old:

• Baby may not need to be admitted if they:

  • Appear well

  • Have normal lab results

  • Have no signs of other infection

• Your provider may still do:

  • Blood and urine tests

  • Inflammatory markers like CRP or procalcitonin (also blood tests)

  • A spinal tap, depending on the situation

Close follow-up is essential if your baby goes home after this visit.

What Should Parents Do If Baby Has a Fever?

• Take a rectal temperature (don’t rely on forehead scanners)

• Call your pediatrician or go to the ER

• Don’t give Tylenol unless directed—we want to see the fever clearly for evaluation

• Trust your gut—you know your baby best

Why We Take Fever Seriously in Babies Under 60 Days

In babies under 2 months, even a low-grade fever can be a sign of something more serious brewing beneath the surface. That’s because their immune systems are still developing and may not respond to infections the way older children and adults do. A baby this young might not show typical signs like fussiness, poor feeding, or sleepiness—fever might be the only clue.

Some of the infections we screen for include:

• Urinary tract infections (common and treatable, but easy to miss without testing)

• Bacteremia, which is bacteria in the bloodstream

• Meningitis, a rare but serious infection around the brain and spinal cord

Because these illnesses can progress quickly in newborns—and because they often don’t look sick at first—pediatricians follow strict fever protocols. That’s why your baby may need blood work, a urine test, or even a spinal tap if they’re under 60 days and running a fever.

It might feel overwhelming in the moment, but this approach gives your baby the safest start and helps doctors catch anything early—before it becomes more serious.

💛 The reassuring part? The vast majority of babies with fever turn out to have something mild like a viral illness or no clear infection at all. Most go on to recover quickly and do just fine. But we never want to miss the chance to treat something that could become dangerous.

Remember, you're not overreacting. You're being a great parent by taking quick action. Most of the time, tests come back normal and no serious infection is found—but we’d rather be safe and sure.

Your pediatrician is always here to help. And you're doing an amazing job!