A rectal temperature of 100.4°F (38°C) or higher means your baby has a fever. What you should do next depends almost entirely on your baby’s age. If your baby is younger than 8 weeks old, a fever at or above 100.4°F needs immediate medical evaluation, even if your baby looks fine. For older infants, most fevers are caused by common viral infections and can be safely managed at home with fluids, comfort, and careful monitoring.
Age Is the Most Important Factor
For babies under 8 weeks old, any fever of 100.4°F or higher is treated as urgent. At this age, a baby’s immune system is still immature, and a fever can signal a serious bacterial infection that isn’t easy to detect just by looking at the baby. The American Academy of Pediatrics has detailed clinical guidelines specifically for infants 8 to 60 days old with fever, because this age group needs careful evaluation even when the baby appears well. Don’t give any fever-reducing medication to infants under 8 weeks. Instead, head to your pediatrician or emergency room right away.
For babies 3 to 6 months old, call your pediatrician if the temperature reaches 102°F (38.9°C) or higher, or if the fever lasts more than 48 hours without any other symptoms like cough or runny nose. Babies in this range are less vulnerable than newborns but still warrant a phone call for higher or persistent fevers.
For babies 6 to 12 months old, fever from a viral illness is common and usually manageable at home. Most of these fevers range between 101°F and 104°F and last two to three days. Contact your doctor if the fever lasts more than three days, returns after being gone for more than 24 hours, or if your baby seems to be getting worse rather than better.
How to Take an Accurate Temperature
A rectal thermometer gives the most reliable reading for babies. If you use an armpit or forehead thermometer and the result seems off, follow up with a rectal reading to confirm. Armpit temperatures are the least accurate of the common methods. Ear thermometers shouldn’t be used until your baby is at least 6 months old, and digital pacifier thermometers and fever strips aren’t recommended at any age.
To take a rectal temperature, apply a small amount of petroleum jelly to the tip of a digital thermometer, lay your baby face-down across your lap, and gently insert the tip about half an inch. Hold it in place until the thermometer beeps. Clean it with rubbing alcohol or soap and water afterward, and label it so it’s only used rectally.
Fever-Reducing Medication by Age
Acetaminophen (Tylenol) can be given to babies 8 weeks and older. Ibuprofen (Advil, Motrin) is not safe for babies under 6 months old unless specifically directed by your pediatrician. Both medications are dosed by weight, not by age, so check the packaging carefully or call your pediatrician for the correct dose if you’re unsure.
You may have heard advice about alternating between acetaminophen and ibuprofen. Pediatric experts have cautioned against this. There’s no evidence that alternating works better than using one medication alone, and the overlapping schedules (one is given every four hours, the other every six) make it easy to lose track and accidentally overdose. Stick with one medication at a time.
Comfort Measures That Help
Keeping your baby hydrated is the single most important thing you can do at home. A fever increases fluid loss, and babies can become dehydrated quickly. If you’re breastfeeding or formula-feeding, offer feeds more frequently than usual. For babies old enough to take other liquids, a pediatric electrolyte solution like Pedialyte helps replace lost fluids. Eating less is normal during illness, but drinking enough is essential.
Dress your baby in a single light layer. Bundling a feverish baby in blankets can trap heat and push the temperature higher. Keep the room comfortable, not cold. A cool washcloth on the forehead can provide some relief if your baby’s skin feels hot. Don’t sponge your baby with cold water or use rubbing alcohol on the skin, both of which can cause shivering and actually raise the body’s core temperature.
Watch for Signs of Dehydration
Fever and dehydration go hand in hand, especially when a baby is also vomiting or has diarrhea. In infants, mild to moderate dehydration shows up as fewer than six wet diapers per day, a dry mouth, fewer tears when crying, and a sunken soft spot on the top of the head. Severe dehydration looks like sunken eyes and only one to two wet diapers in an entire day. If you’re seeing any of these signs, contact your pediatrician promptly.
Symptoms That Need Immediate Attention
The fever number itself matters less than how your baby is acting. A baby with a 103°F temperature who is still making eye contact, drinking fluids, and responding to you is in a very different situation than a baby with 101°F who is limp and unresponsive. Look beyond the thermometer.
Call your pediatrician or seek care if your baby:
- Is unusually sleepy or hard to wake up, or seems floppy and weak
- Refuses two or more feedings in a row or is eating very poorly
- Has trouble breathing, including fast or labored breaths
- Develops a rash that appears quickly, blisters, or looks infected
- Has very loose, watery stools more than three times
- Is crying inconsolably or crying more than usual and can’t be calmed
Get emergency care immediately for seizures, bleeding that won’t stop, or if your baby seems severely ill.
What to Do if Your Baby Has a Seizure
Some babies experience febrile seizures during a fever. These typically last two to three minutes and rarely last longer than ten minutes. They can look terrifying, with shaking, stiffening, or loss of consciousness, but most febrile seizures do not cause lasting harm.
If it happens, note the time it starts. Protect your baby’s head with your hands or something soft, and move any hard or sharp objects away. Do not try to hold your baby still, and do not put anything in their mouth. After the seizure ends, gently roll your baby onto their side in the recovery position. Call your doctor once the seizure is over, or call emergency services if it lasts longer than five minutes.
How Long a Fever Typically Lasts
Most fevers from viral illnesses resolve within two to three days. During that time, the fever may come and go, spiking higher in the evening and improving in the morning. This pattern is normal. Contact your pediatrician if the fever lasts more than three days total, if it disappears for more than 24 hours and then comes back, or if a fever without any other symptoms (no cough, no runny nose, no diarrhea) persists beyond 48 hours. A returning fever can sometimes indicate a secondary infection that developed after the original illness.