A rectal temperature of 100.4°F (38°C) or higher means your baby has a fever. In most cases, a fever is your baby’s immune system doing its job, fighting off an infection. Your main goals are keeping your baby comfortable, watching for warning signs, and knowing which situations require a call to the doctor or a trip to the emergency room.
What Counts as a Fever by Age
For babies, a rectal thermometer gives the most accurate reading. The threshold that matters most depends on how old your baby is:
- Under 3 months: Any rectal temperature of 100.4°F (38°C) or higher requires immediate medical attention. At this age, even a mild fever can signal a serious infection. Don’t wait to see if it resolves on its own.
- 3 to 6 months: A temperature up to 101°F (38.3°C) is concerning if your baby seems unusually irritable, sluggish, or uncomfortable. Anything above 101°F warrants contacting your pediatrician.
- 6 to 24 months: A temperature above 101°F that lasts longer than one day, even without other symptoms, is worth a call to the doctor.
Ear and forehead (temporal artery) thermometers share the same 100.4°F threshold as rectal readings. Armpit temperatures run lower, so 99°F (37.2°C) under the arm is considered a fever. If you’re unsure about your reading, a rectal check is the gold standard for babies.
Keeping Your Baby Comfortable at Home
A fever itself isn’t dangerous in most cases. The goal of home care isn’t necessarily to bring the number down to normal, but to help your baby rest and stay hydrated. Here’s what actually helps:
Fluids first. Fever increases fluid loss, so offer breast milk or formula more frequently than usual. For babies already eating solids, small sips of water or an oral rehydration solution can help. Watch diaper output closely. Fewer than six wet diapers in 24 hours is an early sign of dehydration. If your baby is producing only one or two wet diapers a day, that’s severe dehydration and needs immediate medical attention.
Dress lightly. Don’t bundle a feverish baby in extra blankets or layers. Multiple medical guidelines agree that babies with a fever should not be over-wrapped or under-dressed. A single comfortable layer is usually right. If your baby is already bundled up, simply removing the extra layers can help them feel better.
Skip the sponge bath. Tepid sponge baths used to be a go-to recommendation, but major pediatric guidelines no longer recommend them for treating fever. They can cause shivering, which actually raises body temperature. Alcohol baths are also unsafe for babies and should never be used.
Keep the room comfortable. A slightly cool room with good airflow helps more than piling on cooling measures. Let your baby rest as much as they want, and hold or cuddle them if that’s what soothes them.
Fever-Reducing Medication
Acetaminophen (Tylenol) can be given to babies, but for children under 2 years old, you should get dosing guidance from your pediatrician first. The liquid form comes as 160 mg per 5 mL, and the correct dose is based on your baby’s weight, not their age. If you don’t know your baby’s current weight, your doctor’s office can help you figure out the right amount.
Ibuprofen (Advil, Motrin) should not be given to babies under 6 months old. For babies older than 6 months, it’s an option, but again, check with your pediatrician for the correct dose if your baby is under 2 years or weighs less than 12 pounds.
Never give aspirin to a baby, child, or teenager. Aspirin use during a viral illness has been linked to Reye’s syndrome, a rare but serious condition that causes swelling in the liver and brain.
When to Call Your Pediatrician
The urgency depends on your baby’s age and how long the fever has lasted:
- Under 12 weeks: Call immediately or go to urgent care for any fever of 100.4°F or higher, even if your baby seems fine otherwise. Babies this young need testing to rule out serious infections.
- 3 to 6 months: Contact your doctor within 24 hours if your baby has a fever, especially if they seem fussy or lethargic.
- 6 to 12 months: Contact your doctor within 24 hours if the fever exceeds 101°F and lasts more than a day with no other obvious cause like a cold or cough.
- Any age: A fever lasting more than 3 days needs medical evaluation.
Signs That Need Emergency Care
Most fevers are caused by common viral infections and resolve on their own. But certain symptoms alongside a fever can point to something more serious, like meningitis or sepsis. Head to the emergency room if your baby has any of the following:
- A bulging soft spot on the top of the head
- Stiffness in the neck or body
- Extreme sleepiness or difficulty waking up
- Constant, inconsolable crying
- Refusal to eat or inability to keep fluids down
- A purple or red rash that doesn’t fade when you press on it
- Limp, unresponsive, or unusually inactive behavior
Any one of these combined with a fever is enough to seek emergency care. Trust your instincts. If something about your baby’s behavior feels wrong, even if you can’t pinpoint exactly what, it’s always reasonable to get them evaluated.
What to Do if Your Baby Has a Seizure
Febrile seizures happen in some children when their temperature spikes. They look frightening, but most are harmless and last fewer than five minutes. If your baby has a seizure during a fever, here’s what to do:
- Gently place your baby on the floor, not on a bed, table, or in your arms.
- Turn them onto their side to prevent choking on saliva or vomit.
- Do not try to hold them down or restrain their movements.
- Do not put anything in their mouth.
If the seizure lasts longer than five minutes, call 911. After any febrile seizure, even a short one, contact your pediatrician. A first-time seizure will typically need a medical evaluation to rule out other causes, but most febrile seizures don’t lead to lasting problems.