Baby Fever: When to Watch, When to Call, and When to Go to the ER
Fever in a baby is about age and behavior, not just the number. The under-3-months rule, key warning signs, and when it's an ER trip.
Baby Fever: When to Watch, When to Call, and When to Go to the ER
A hot little forehead at 2 a.m. can send anyone into a spiral. Fever itself isn't a disease — it's a sign the body is fighting something. What matters most is your baby's age and how they're acting, not the exact number on the thermometer.
First, what counts as a fever
A fever is a temperature of 100.4°F (38°C) or higher. For babies, a rectal reading is the most accurate, and it's the number your pediatrician will want for a young infant. Ear thermometers aren't reliable under 3 months.
The one hard rule: under 3 months
If your baby is younger than 3 months with a rectal temperature of 100.4°F or higher, call your pediatrician or go to the ER right away — even at night, even if the baby otherwise seems fine. In this age group a fever can be the only clue to a serious infection, and young infants need to be checked promptly. Don't reach for fever medicine to buy time first; get them seen.
3 months to about 3 years
For older babies, the whole picture matters more than the number. Many fevers come from ordinary viruses and pass in a few days. Call your pediatrician if:
- The fever reaches 102°F or higher, or lasts more than a couple of days.
- Your baby has fewer wet diapers, a dry mouth, or no tears — signs of dehydration.
- They're unusually sleepy, inconsolable, or just "not themselves."
- The fever comes with an earache, a rash, vomiting, or a lingering cough.
Go to the ER or call 911 for these
- Trouble breathing, or lips or face turning blue or gray.
- A stiff neck, a bulging soft spot, or a rash of tiny bruise-like spots that don't fade when pressed.
- A seizure, or a baby who is limp, unresponsive, or very hard to wake.
- Any fever in a baby with a serious medical condition you've been told to watch closely.
Keeping your baby comfortable
Focus on comfort, not on chasing a "normal" number. Offer extra breast milk or formula to keep them hydrated, dress them in light layers, and keep the room cool. Never give aspirin to a child. Acetaminophen usually isn't given under 3 months, and ibuprofen not until 6 months, without your doctor's okay — and because dosing is by weight, ask your pediatrician for the right amount for your baby.
Trust your instincts. You know your baby better than any chart, and pediatric offices genuinely expect and welcome the "should I be worried?" call — so when something feels off, make it.