A rectal temperature of 100.4°F (38°C) or higher counts as a fever in babies. What you should do depends almost entirely on your baby’s age and how they’re acting. For any baby under 3 months old, a temperature of 100.4°F or above is an automatic call to the pediatrician or a trip to the emergency room, no matter how well they seem. For older babies, you have more room to manage things at home while watching for specific warning signs.
Age Changes Everything
The younger your baby, the more seriously a fever needs to be taken. Here’s how the thresholds break down:
- Under 3 months: Any rectal temperature of 100.4°F (38°C) or higher needs immediate medical evaluation. At this age, a fever can be the only sign of a serious bacterial infection, and doctors will want to run tests even if your baby looks fine. Don’t give fever-reducing medicine first and wait to see what happens. Go straight to your pediatrician or the ER.
- 3 to 6 months: A temperature up to 101°F (38.3°C) can often be monitored at home, but call your pediatrician if your baby seems unusually irritable, sluggish, or uncomfortable. Any temperature above 101°F at this age warrants a call regardless of how they’re acting.
- 6 to 24 months: A temperature above 101°F that lasts longer than one full day needs a pediatrician’s attention, even if your baby has no other symptoms. If other symptoms like rash, vomiting, or ear pulling are present, call sooner.
How to Take an Accurate Temperature
A rectal reading is the most reliable method for babies and the one pediatricians base their guidelines on. Forehead, armpit, and ear thermometers are convenient, but they can read a degree or more off in either direction. That margin matters when you’re deciding whether a 3-week-old needs the emergency room.
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 or on a firm surface, and insert the tip about half an inch. Hold it in place until it beeps. If you’ve been using a forehead or armpit thermometer and the reading is borderline, confirm it rectally before making decisions.
Comfort Measures That Actually Help
A fever itself isn’t dangerous in most cases. It’s your baby’s immune system fighting off an infection. The goal of home care isn’t to eliminate the fever entirely but to keep your baby comfortable and hydrated while their body does its job.
Dress your baby in one light layer. Piling on blankets to “sweat out” a fever traps heat and can push the temperature higher. Keep the room at a normal, comfortable temperature.
Offer fluids frequently. Breast milk or formula works for babies under 6 months. Older babies can also have small sips of water or an oral rehydration solution. Fevers increase fluid loss, and dehydration can set in faster than you’d expect. A well-hydrated baby should produce at least six wet diapers in 24 hours. Fewer than three wet diapers in a day, or none in eight hours, is a sign of dehydration that needs a pediatrician’s attention right away.
A lukewarm sponge bath can bring temporary relief, but it works best when combined with fever-reducing medicine. On its own, the temperature tends to bounce right back up once you stop. Never use cold water, ice packs, or rubbing alcohol. These trigger shivering, which actually raises your baby’s core temperature and makes things worse.
Fever-Reducing Medicine by Age
Acetaminophen (Tylenol) can be given every 4 to 6 hours, but not to babies younger than 3 months without a doctor’s specific instruction. Ibuprofen (Advil, Motrin) can be given every 6 to 8 hours, but not to babies younger than 6 months without a doctor’s order. Never give aspirin to any child.
Dosing is based on your baby’s weight, not their age. The concentration of the liquid matters too. Infant acetaminophen suspension is typically 160 mg per 5 mL. A baby weighing 12 to 17 pounds gets 2.5 mL, while a baby weighing 18 to 23 pounds gets 3.75 mL. For ibuprofen, a baby weighing 18 to 23 pounds gets 3.75 mL of the standard 100 mg per 5 mL suspension. Check the label on whatever product you have at home, because concentrations can vary. If you’re unsure, call your pediatrician’s office for the exact dose.
One important note: the point of medicine is comfort, not hitting a specific number on the thermometer. If your baby has a fever of 101°F but is playing, eating, and sleeping normally, they may not need medicine at all. If they’re miserable and refusing to eat, medicine can help them rest and stay hydrated.
Warning Signs That Need Emergency Care
Most fevers in babies are caused by common viral infections and resolve within a few days. But certain symptoms alongside a fever signal something more serious. Call 911 if your baby:
- Can’t wake up or is extremely difficult to rouse
- Is too weak to move or stand (for older babies)
- Has severe trouble breathing, struggling with each breath
- Develops purple or blood-colored spots or dots on the skin
Head to the emergency room if your baby:
- Has a stiff neck and can’t move it normally
- Has a bulging or swollen soft spot on the head (for babies under 1 year)
- Seems “out of it” or not alert when awake
- Has a seizure during the fever
What Febrile Seizures Look Like
Some babies and toddlers have seizures triggered by a rapid rise in body temperature. These are called febrile seizures, and while they look terrifying, the most common type lasts a few seconds to 15 minutes and doesn’t cause lasting harm. During a febrile seizure, your baby may stiffen, twitch, or roll their eyes back.
If it happens, lay your baby on their side on a flat surface, away from anything they could hit. Don’t put anything in their mouth. Time the seizure. If it lasts longer than five minutes, call 911. Even if the seizure stops quickly on its own, take your baby to be evaluated afterward, especially if it’s the first time it’s happened. Febrile seizures don’t mean your child has epilepsy, and most children who have one never have another.
How Long a Fever Should Last
A typical viral fever lasts two to three days, though some can stretch to five. For children under 2, a fever lasting more than 24 hours warrants a call to the pediatrician even if no other symptoms are present. For older toddlers, the threshold is generally around three days. A fever that goes away and then comes back after a day or two is also worth reporting, since it can indicate a secondary infection like an ear infection or urinary tract infection that may need treatment.
Between fever episodes, pay more attention to how your baby is acting than to the number on the thermometer. A baby with a 102°F fever who is alert, making eye contact, and taking fluids is in a very different situation than a baby with a 100.5°F fever who is limp and unresponsive. Behavior is a better barometer than temperature alone.