Baby Fever: When to Call the Doctor

Few things make a parent's heart race quite like touching your baby's forehead and realizing they feel warm. A baby fever can be scary, especially the first time it happens. The good news is that fevers are actually a normal part of how the body fights off infection, and most of the time, they resolve on their own. That said, knowing what counts as a fever, how to check your baby's temperature, and when to call the doctor can help you feel a lot more confident.

What Counts as a Fever in Babies?

A baby's normal body temperature can vary a little depending on the time of day, how active they have been, and even what they are wearing. In general, the American Academy of Pediatrics (AAP) considers a rectal temperature of 100.4°F (38°C) or higher to be a fever.

It is worth noting that different thermometer methods can give slightly different readings. A rectal thermometer tends to be the most accurate for infants. If you are using a forehead or underarm thermometer, keep in mind that the reading may be slightly lower than the actual core temperature. Your pediatrician can help you understand what the numbers mean for the specific method you use.

For newborns under 3 months, any fever of 100.4°F or above is considered urgent. This is because very young babies have immature immune systems, and a fever at this age can sometimes signal a serious infection. If your newborn has a rectal temperature at or above 100.4°F, call your pediatrician right away or head to the emergency room.

How to Take Your Baby's Temperature

Getting an accurate temperature reading on a wiggly baby can feel tricky, but it gets easier with practice. Here are the most common methods parents use.

Rectal thermometer (most accurate for babies under 6 months)

Apply a small amount of petroleum jelly to the tip of a digital rectal thermometer. Lay your baby on their back or tummy and gently insert the tip about half an inch. Hold it in place until the thermometer beeps. Many parents find this method less intimidating than it sounds, and most babies tolerate it well.

Temporal artery (forehead) thermometer

These are quick and non-invasive, which many parents appreciate. Simply swipe the thermometer across your baby's forehead following the manufacturer's instructions. While convenient, these can sometimes read a little lower than rectal, so mention the method when you talk to your pediatrician.

Underarm (axillary) thermometer

Place a digital thermometer snugly in your baby's armpit and hold their arm gently against their body until it beeps. This method is the least accurate and typically reads about 1 degree lower than rectal. It can be a good quick-check option, but if the reading seems elevated, you may want to follow up with a rectal reading for confirmation.

Common Causes of Baby Fever

Fevers in babies can happen for a number of reasons. Some of the most common include viral infections like colds or stomach bugs, ear infections, urinary tract infections, and the body's normal response after vaccinations. Some babies may also run a mild temperature when they are teething, though most pediatricians agree that teething alone does not cause a true fever above 100.4°F.

Occasionally, overdressing a baby or spending time in a very warm environment can raise their body temperature temporarily. If you suspect your baby might be overdressed, try removing a layer and rechecking in about 15 to 20 minutes.

Every baby is different, and the cause of a fever is not always obvious. That is completely normal. If you are unsure what is going on, your pediatrician is always a great resource.

When to Call Your Pediatrician

Knowing when to pick up the phone can save you a lot of worry. Here are some general guidelines that many pediatricians share with parents.

Call right away or go to the ER if:

Your baby is under 3 months old and has a rectal temperature of 100.4°F or higher. Your baby is 3 to 6 months old and has a temperature of 102°F or higher. Your baby has a fever that lasts more than 24 hours (for babies under 2 years). Your baby seems unusually sleepy, limp, or hard to wake. Your baby has trouble breathing, is not eating, or shows signs of dehydration like fewer wet diapers, no tears when crying, or a dry mouth. Your baby has a febrile seizure (shaking or jerking movements), which can be frightening but is usually not harmful. Still, always seek medical attention afterward.

Call during office hours if:

Your baby is over 6 months old with a fever under 102°F and is otherwise acting like themselves, eating and drinking, and having normal wet diapers. The fever has lasted more than a day or two and you want guidance. You just want reassurance or have questions about medication dosing. There is absolutely nothing wrong with calling your pediatrician for peace of mind.

Trust your instincts. You know your baby best. If something feels off, even if the fever number does not seem very high, it is always okay to call.

How to Keep Your Baby Comfortable

When your baby has a fever, your main goal is to help them feel as comfortable as possible while their body does its work. Here are some things many parents find helpful.

Dress your baby in lightweight clothing. A single layer and a light blanket is usually enough. Overdressing can trap heat and make the fever feel worse. Offer plenty of fluids. If your baby is under 6 months, that means breast milk or formula. For older babies, you can also offer small sips of water. Keeping them hydrated is one of the most important things you can do. You can track feedings and wet diapers to make sure they are getting enough.

A lukewarm (not cold) sponge bath can sometimes help bring a slight fever down and make your baby more comfortable. Avoid cold water or ice baths, as these can cause shivering, which actually raises body temperature.

Keep the room at a comfortable temperature, not too warm and not too cold. A fan on low can help circulate air, but do not point it directly at your baby.

What Not to Do When Baby Has a Fever

It is just as important to know what to avoid. Never give aspirin to a baby or child, as it has been linked to a rare but serious condition called Reye's syndrome. Do not give fever-reducing medication to babies under 3 months without talking to your pediatrician first. Avoid rubbing alcohol baths, which were once recommended but can be dangerous for babies. And do not bundle your baby up in extra blankets thinking they need to "sweat it out." This old wives' tale can actually make things worse.

If your pediatrician recommends infant acetaminophen or ibuprofen (for babies 6 months and older), always dose based on your baby's weight, not their age. Your doctor or pharmacist can help you figure out the right amount.