A rectal temperature of 100.4°F (38°C) or higher counts as a fever in babies. What you should do depends largely on your baby’s age: a fever in a newborn under 3 months old needs immediate medical attention, while older babies can often be kept comfortable at home with fluids, light clothing, and, when appropriate, fever-reducing medication. Here’s how to handle it step by step.
Age Matters More Than the Number
The same temperature reading can mean very different things depending on how old your baby is. These age-based thresholds, based on rectal temperature, guide when to call your pediatrician or head to the emergency room:
- Under 3 months: Any rectal temperature of 100.4°F (38°C) or higher needs a same-day medical evaluation. Do not give fever-reducing medication first. Call your pediatrician or go to the ER.
- 3 to 6 months: A temperature up to 101°F (38.3°C) may not require a visit on its own, but call your pediatrician if your baby seems unusually irritable, sluggish, or uncomfortable. Any temperature above 101°F at this age warrants a call.
- 6 to 24 months: A temperature above 101°F that lasts longer than one day without other symptoms is worth a call. If your baby is acting relatively normal, eating, and staying hydrated, you can usually manage the fever at home while monitoring closely.
Taking an Accurate Temperature
For babies, a rectal thermometer gives the most reliable reading. Digital thermometers work quickly and are inexpensive. Apply a small amount of petroleum jelly to the tip, insert it about half an inch, and hold it in place until it beeps. Forehead and ear thermometers are convenient but less accurate in infants, which matters when you’re close to a threshold like 100.4°F. If you get a concerning reading from a forehead thermometer, confirm it rectally before deciding your next step.
Keeping Your Baby Comfortable
A fever is your baby’s immune system doing its job. The goal isn’t necessarily to eliminate the fever entirely but to help your baby rest and stay hydrated while their body fights off the infection.
Clothing and Room Temperature
Dress your baby in lightweight, breathable fabrics like cotton. A single layer or just a diaper and a sleeveless onesie is often enough. Bundling a feverish baby in extra blankets traps heat and can push their temperature higher. Keep the room between 68°F and 72°F. Signs your baby is too warm include sweating, flushed cheeks, and skin that feels hot to the touch even beyond the fever itself.
Fluids
Fever increases fluid loss through sweat and faster breathing, so dehydration is a real concern. Offer breast milk or formula more frequently than usual. Babies over 6 months can also have small sips of water. A well-hydrated baby produces six to eight wet diapers a day. Fewer than three or four wet diapers in 24 hours is a sign of dehydration and a reason to call your pediatrician.
Skip the Cold Baths
It’s tempting to cool a feverish baby down with a cold or lukewarm bath, but research shows that sponge baths cause significantly more distress in feverish children without reliably reducing temperature. Cold water can also trigger shivering, which actually raises core body temperature. Current pediatric guidance discourages physical cooling methods for ordinary fevers. If your baby enjoys a warm bath as part of their routine, that’s fine for comfort, but don’t use it as a fever treatment.
When to Use Fever-Reducing Medication
Medication isn’t always necessary. If your baby is older than 3 months, feeding well, and not in obvious distress, you can hold off and simply monitor. But if your baby is clearly uncomfortable, having trouble sleeping, or refusing to eat, a fever reducer can help.
Acetaminophen (Tylenol) is safe for babies 3 months and older. You can give it every 4 to 6 hours as needed, up to 5 times in 24 hours. Ibuprofen (Advil, Motrin) is only safe for babies 6 months and older and can be given every 6 to 8 hours, up to 4 times in 24 hours. Never give ibuprofen to a baby under 6 months. It hasn’t been found safe for that age group and isn’t FDA-approved for them.
Both medications are dosed by weight, not age. The weight printed on your baby’s medicine syringe or packaging determines the correct amount. If you’re unsure of the right dose, call your pediatrician’s office rather than guessing. An incorrect dose is one of the most common medication errors parents make during fevers.
Don’t Alternate Medications Without Guidance
You may have heard advice about switching back and forth between acetaminophen and ibuprofen. The American Academy of Pediatrics recommends sticking with a single medication at the correct dose and frequency. Alternating the two creates confusing dosing schedules that increase the risk of accidentally exceeding the safe daily maximum of one or both drugs, or giving a double dose of the same one. If a single medication isn’t controlling your baby’s discomfort, talk to your pediatrician before adding a second one.
Signs That Need Emergency Care
Most fevers in babies are caused by common viral infections and resolve on their own within a few days. But certain signs alongside a fever signal something more serious.
Lethargy is different from sleepiness. A lethargic baby stares into space, won’t smile, barely responds to you, and may be too weak to cry or difficult to wake. This is an emergency. Breathing problems are another red flag: fast breathing, grunting with each breath, bluish lips, or skin pulling inward between the ribs (called retractions). A baby with severe breathing difficulty won’t be able to drink, cry, or make normal sounds.
Watch for rashes, specifically purple or blood-red spots or dots on the skin. When these appear alongside a fever, they can indicate a serious bloodstream infection. You can test a rash by pressing on it gently. Normal viral rashes fade under pressure. Purple or red spots that stay the same color when pressed need immediate evaluation.
Other reasons to seek emergency care include a fever above 104°F at any age, a seizure (even a brief one), signs of dehydration that don’t improve with feeding (dry mouth, no tears when crying, sunken soft spot on the head), or a fever that persists beyond three days without improvement.
What to Expect Over the Next Few Days
Most fevers from viral illnesses peak on the second or third day and then gradually come down over 3 to 5 days. It’s normal for the temperature to go up and down during that window, often spiking higher in the late afternoon and evening. This pattern doesn’t mean your baby is getting worse.
Focus less on the exact number on the thermometer and more on how your baby is acting. A baby with a 102°F fever who is still making eye contact, taking fluids, and having wet diapers is generally in a safer position than a baby with a 100.5°F fever who is limp and refusing to eat. Your baby’s behavior is the most reliable guide to how sick they actually are.