If your infant has a fever, the single most important factor is age. A rectal temperature of 100.4°F (38°C) or higher in a baby younger than 3 months old requires an immediate call to your pediatrician, even if your baby looks fine. For older infants, you generally have more room to monitor symptoms at home and focus on comfort. Here’s what to do at each stage.
How to Take an Accurate Temperature
A rectal thermometer is the most accurate way to measure an infant’s temperature, especially for babies under 3 months. Forehead and ear thermometers can be convenient, but they’re less reliable at this age and can miss a true fever or falsely flag one.
To take a rectal temperature, use a digital thermometer with a short probe. Apply a small amount of petroleum jelly to the tip, lay your baby belly-down on a firm surface, and insert the probe gently about half an inch. Hold it in place until it beeps. Label this thermometer so it’s never accidentally used in the mouth, since it can transfer bacteria from stool.
When a Fever Needs Medical Attention
Age changes the risk profile of a fever dramatically. The American Academy of Pediatrics has specific evaluation guidelines for infants 8 to 60 days old with a temperature at or above 100.4°F because young babies have immature immune systems and can deteriorate quickly from bacterial infections that older children fight off easily.
- Under 3 months: Any rectal temperature of 100.4°F (38°C) or higher warrants a call to your doctor right away, day or night. Do not give fever-reducing medication first and wait to see what happens. Your pediatrician needs to evaluate the baby, and in many cases will order blood and urine tests to rule out serious infection.
- 3 to 6 months: A temperature up to 101°F (38.3°C) can often be monitored at home if your baby is acting normally, feeding well, and making eye contact. Call your doctor if your baby seems unusually irritable, lethargic, or uncomfortable, or if the temperature rises above 101°F.
- 6 to 24 months: A temperature above 101°F (38.3°C) that lasts longer than one day without other symptoms is worth a call. If your baby has additional signs like vomiting, diarrhea, rash, or difficulty breathing, call sooner.
Regardless of age, seek emergency care if your baby has a seizure, is unresponsive or extremely difficult to wake, has a stiff neck, develops purple or red spots on the skin that don’t fade when you press on them, or is breathing very rapidly or struggling to breathe.
Keeping Your Baby Comfortable at Home
Fever itself is not dangerous in most cases. It’s the body’s way of fighting infection. Your goal at home isn’t necessarily to bring the number on the thermometer down to normal. It’s to keep your baby comfortable, hydrated, and rested while the immune system does its work.
Dress your baby in a single light layer of clothing. Bundling a feverish baby in blankets can trap heat and push the temperature higher. A light cotton onesie or sleep sack is usually enough. Keep the room at a comfortable temperature rather than making it especially warm or cold.
Offer frequent feedings. Breast milk or formula provides both hydration and calories. Babies with fevers lose fluid faster through sweating and rapid breathing, so shorter, more frequent feeds help prevent dehydration. Track wet diapers to gauge hydration: infants should produce at least six wet diapers per day. If you’re seeing only one or two wet diapers in a day, that’s a sign of dehydration and a reason to call your doctor.
Other signs of dehydration to watch for include a sunken soft spot on the top of the head, dry mouth, no tears when crying, and unusual sleepiness. These warrant a prompt call to your pediatrician.
Fever-Reducing Medication for Infants
Acetaminophen (Tylenol) is the standard fever reducer for infants, available as a liquid at a concentration of 160 mg per 5 mL. The dose is based on your baby’s weight, not age, so check the packaging or ask your pediatrician for the correct amount. You can give it every 4 hours as needed, with a maximum of 5 doses in 24 hours. However, acetaminophen should not be given to babies under 2 months without a doctor’s guidance.
Ibuprofen (Motrin, Advil) is not safe for babies under 6 months old. It has not been found to be safe in that age group and is not FDA-approved for use before 6 months. Once your baby is 6 months or older, ibuprofen can be given every 6 to 8 hours as needed, again dosed by weight.
Never give aspirin to an infant or child. Aspirin use during a viral illness is linked to Reye’s syndrome, a rare but life-threatening condition that causes swelling in the liver and brain. Without proper treatment, Reye’s syndrome can be fatal within days. This risk is highest during flu and chickenpox infections, but the safest approach is to avoid aspirin entirely in children and teenagers.
What Not to Do
A few common instincts can actually make things worse. Don’t put your baby in a cold bath or sponge them down with rubbing alcohol. Cold water causes shivering, which raises core body temperature. Rubbing alcohol can be absorbed through the skin and is toxic.
Don’t alternate between acetaminophen and ibuprofen unless your pediatrician specifically tells you to. It’s easy to lose track of timing and accidentally overdose. Stick with one medication at the recommended intervals.
Don’t rely on how warm your baby’s forehead feels to your hand. A baby can feel warm from crying, being overdressed, or sitting in a car seat on a hot day. Always confirm with a thermometer before deciding whether you’re dealing with a true fever.
How Long a Fever Typically Lasts
Most infant fevers are caused by common viral infections and resolve within 3 to 5 days. The fever may come and go during that window, spiking higher in the evening and dropping in the morning. This pattern is normal and doesn’t mean the infection is getting worse.
A fever that lasts beyond 5 days, keeps climbing despite medication, or is accompanied by new symptoms like a rash, persistent vomiting, or ear tugging deserves a follow-up with your pediatrician. Even if you’ve already called once, it’s reasonable to call again if the pattern changes or your baby seems worse.