A fever in a baby is a temperature of 100.4°F (38°C) or higher, measured rectally. Most infant fevers are caused by common viral infections and resolve within a few days with simple comfort measures at home. The key is knowing which steps actually help, which ones to skip, and when a fever signals something that needs medical attention right away.
Check the Temperature Accurately
Before anything else, get a reliable reading. For babies 3 months and younger, a rectal thermometer is the only method accurate enough to trust. You can add a forehead thermometer starting at 3 months, and an ear thermometer becomes useful around 6 months. Armpit readings are convenient but consistently less accurate, so they’re not ideal when precision matters most.
To take a rectal temperature, apply a small amount of petroleum jelly to the tip of a standard digital thermometer and insert it about half an inch. Hold it in place until it beeps. The number you get is the most reliable reading available for young children.
Know When It’s an Emergency
Your baby’s age changes everything about how seriously to treat a fever. These thresholds are worth memorizing:
- Under 3 months: Any fever of 100.4°F or higher needs immediate medical attention, even if your baby seems fine otherwise. At this age, fever can signal a serious infection that requires testing.
- 3 to 6 months: Call your pediatrician for any temperature above 100.4°F, or for a lower temperature if your baby seems unusually sick or fussy.
- 6 to 24 months: A fever above 100.4°F that lasts more than one day warrants a call. A temperature of 103°F or higher at any point deserves medical advice.
Regardless of age, get emergency care if your baby has trouble breathing, skin or lips that look blue or gray, seems unusually limp or hard to wake, or is vomiting repeatedly. A rash that appears suddenly alongside a fever, especially one that blisters or looks infected, also warrants a prompt call.
Why Fever Itself Isn’t the Enemy
Fever is part of your baby’s immune defense. It creates a less hospitable environment for viruses and bacteria, and experimental studies show that this inflammatory response genuinely benefits the body during infection. For decades, parents have been taught to fear fever itself, but the temperature number alone rarely causes harm. What matters far more is how your baby looks and acts. A baby with a 102°F fever who is still making eye contact, feeding, and producing wet diapers is generally in better shape than a baby with 100.5°F who is limp and unresponsive.
This doesn’t mean you should ignore fever or let your baby suffer. It means the goal of treatment is comfort, not forcing the number back to 98.6°F.
Keep Your Baby Comfortable
Simple environmental changes make a real difference. Keep the room between 68 and 72°F. Dress your baby in a single layer of cotton, like a light onesie or cotton pajamas. Piling on blankets to “sweat out” a fever doesn’t help and can actually trap heat.
Hydration is critical. A feverish body loses fluid faster than normal. For babies under 6 months, offer breast milk or formula more frequently than usual. Older babies can also have small sips of water. Watch for signs of dehydration: fewer wet diapers than normal, crying with fewer tears, a dry mouth, or a sunken soft spot on the head. These are reasons to call your pediatrician promptly.
When to Use Fever-Reducing Medicine
Acetaminophen (Tylenol) is the standard fever reducer for infants, but it should not be given to babies under 2 months without a doctor’s guidance. For children under 2 years old, checking with your pediatrician before giving acetaminophen is generally recommended to make sure the dose is correct for your baby’s weight. Pediatric liquid acetaminophen comes in a standardized concentration of 160 mg per 5 mL, which reduces the risk of dosing errors.
Ibuprofen (Motrin, Advil) is only safe for babies 6 months and older. For most children over 6 months, starting with either acetaminophen or ibuprofen alone is the right first step. You may have heard about alternating the two medicines. While this can lower a stubborn fever more effectively, the American Academy of Pediatrics notes it also raises the risk of accidentally giving too much of one or both. Alternating should only be done with specific instructions from your pediatrician and a written dosing schedule you can follow carefully.
Give no more than 5 doses of acetaminophen in 24 hours, spaced at least 4 hours apart. Avoid combination products (medicines with more than one active ingredient) for children under 6. And never give aspirin to a baby or child.
How to Give a Sponge Bath Safely
If medicine alone isn’t bringing enough relief and your baby is still uncomfortable, a lukewarm sponge bath can help. Wait at least 30 minutes after giving fever-reducing medicine before trying this, so the medicine has time to work first.
Use water between 90°F and 95°F, which feels barely warm to your wrist. Sponge your baby gently for 20 to 30 minutes. Stop immediately if your baby starts shivering, because shivering actually raises the body’s core temperature and works against what you’re trying to do. Never use cold water, ice, or rubbing alcohol. These cool the skin too rapidly and can cause a dangerous drop in body temperature.
If your baby clearly hates the sponge bath or doesn’t seem to feel better afterward, there’s no benefit to repeating it.
What a Normal Fever Timeline Looks Like
Most viral fevers in babies follow a predictable arc. The temperature typically peaks in the late afternoon or evening, dips overnight, and may climb again the next day. This cycling pattern is normal and doesn’t mean your baby is getting worse. A typical viral fever lasts two to three days, though some can stretch to five.
Call your pediatrician if a fever in a baby 6 months or older persists beyond three days, even if it’s not dangerously high. Duration matters because it can indicate a bacterial infection or another condition that needs treatment beyond home care.
Between temperature checks, the most useful thing you can monitor is your baby’s behavior. A baby who is feeding reasonably well, making wet diapers, and has periods of alertness is generally handling the illness well. A baby who becomes increasingly difficult to wake, goes limp, cries inconsolably, or stops producing wet diapers is showing signs that something more serious may be happening.