A baby has a fever when their rectal temperature reaches 100.4°F (38°C) or higher. What you should do depends mostly on your baby’s age and how they’re acting. For babies under 3 months old, any fever is a reason to call your pediatrician right away, even if your baby seems fine. For older infants, the situation is usually less urgent, and home care is often enough.
How to Take an Accurate Temperature
A rectal thermometer is the most accurate option for babies, especially those younger than 3 months. Forehead (temporal) thermometers work well for babies 3 months and older. Ear thermometers aren’t considered accurate until after 6 months of age. Armpit readings are the least reliable of all methods, though they can serve as a quick first check when your baby seems off.
If you get a concerning armpit reading, follow up with a rectal measurement before making decisions. The thresholds differ slightly by method: 100.4°F rectally, 100°F orally, and 99°F under the arm all qualify as a fever.
Age-Based Rules for Calling the Doctor
Your baby’s age changes everything about how seriously to treat a fever. A newborn’s immune system is still developing, so infections can escalate quickly in ways they wouldn’t in an older baby.
- Under 3 months: Call your doctor for any fever of 100.4°F or higher, regardless of other symptoms. The American Academy of Pediatrics has specific evaluation guidelines for febrile infants as young as 8 days old because fever at this age can signal a serious infection that needs testing.
- 3 to 6 months: Call if the temperature reaches 100.4°F or higher, or if it’s below that threshold but your baby seems unusually sick or irritable.
- 6 to 24 months: Call if the fever is above 100.4°F and lasts longer than one day.
- Any age: Call if a fever persists for more than three days.
Signs That Need Emergency Care
Most fevers in babies are caused by common viral infections and resolve on their own. But certain symptoms alongside a fever mean you should get medical help immediately, not wait for a callback. Watch for trouble breathing, skin or lips that look blue, purple, or gray, seizures, difficulty swallowing (sometimes showing up as unusual drooling), or a baby who seems unresponsive or unusually hard to wake.
Fussiness or pain that keeps getting worse and won’t let up also warrants urgent attention, as does repeated vomiting, especially after a fall or head bump.
Keeping Your Baby Comfortable at Home
For older babies whose fever doesn’t hit the thresholds above, the goal is comfort, not necessarily bringing the number on the thermometer down to normal. Fever itself is part of the body’s immune response and isn’t inherently dangerous at moderate levels.
Dress your baby in lightweight clothing and keep the room at a comfortable temperature. Offer frequent feedings, whether breast milk, formula, or water for babies old enough to drink it. Small, frequent sips are easier to keep down than large volumes at once. You may notice your baby wants to nurse or bottle-feed more often than usual, which is actually helpful since it keeps fluid intake up.
You might have heard that a lukewarm sponge bath can help bring down a fever. Research comparing sponge baths plus fever-reducing medication to medication alone found no meaningful temperature difference after two hours. Babies in the sponge bath group did, however, show significantly higher discomfort scores. In other words, the bath made them more miserable without making them better. Skip it unless your pediatrician specifically recommends it.
Fever-Reducing Medication
For babies under 2 years old, check with your doctor before giving acetaminophen (Tylenol) to make sure you’re using the correct dose. The liquid form comes in a concentration of 160 mg per 5 mL, and dosing is based on your baby’s weight, not their age. If your doctor gives the go-ahead, it can be given every 4 hours as needed, with a maximum of 5 doses in 24 hours.
Ibuprofen (Motrin, Advil) should not be given to babies under 6 months old. After 6 months, it’s an option, but again, check with your provider first for babies under 2 or those weighing less than 12 pounds.
Never give a baby or child aspirin. Aspirin in children is linked to Reye’s syndrome, a rare but life-threatening condition that causes swelling in the liver and brain. This applies to plain aspirin and any medication that contains aspirin as an ingredient.
Watching for Dehydration
Fever increases the amount of fluid your baby loses, so dehydration is the most common complication to watch for. The signs in a baby are specific and worth memorizing: fewer wet diapers than usual, a sunken soft spot on the top of the head, sunken eyes, few or no tears when crying, and unusual drowsiness or irritability.
If you notice any of these, contact your doctor promptly. Dehydration in infants can progress faster than in older children because babies have smaller fluid reserves relative to their body size. Keeping up with regular feedings is the simplest prevention.
What to Do During a Febrile Seizure
Febrile seizures happen in about 3 to 4 out of every 100 children. They’re triggered by a rapid rise in body temperature and are frightening to witness but rarely cause lasting harm. If your baby has one, place them on the floor or a bed away from hard or sharp objects and turn their head to the side so saliva or vomit can drain. Do not put anything in their mouth. Call your pediatrician once the seizure stops. If it lasts longer than 5 minutes, call 911.