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. For any baby under 3 months old, a fever at or above that threshold is an emergency that requires an immediate trip to the ER, no exceptions. For older babies, you can often manage a fever safely at home with the right approach.
Why Age Matters More Than the Number
A 101°F fever in a 4-month-old and a 101°F fever in a newborn are very different situations. Newborns have immature immune systems, which means a fever can be the only early sign of a serious bacterial infection. Babies under 2 months with a rectal temperature of 100.4°F or higher need emergency evaluation right away, even if they seem fine otherwise. Don’t wait to see if it comes down on its own, and don’t give fever-reducing medicine first.
For babies between 3 and 6 months old, call your pediatrician if the rectal temperature is higher than 102°F (38.9°C), or if the fever is lower but your baby seems unusually irritable, sluggish, or uncomfortable. For babies 6 months and older, fever alone is less concerning. Focus on how your baby is acting rather than the exact number on the thermometer. A baby who is still alert, making eye contact, and taking fluids is generally handling the fever well.
How to Take an Accurate Temperature
For babies under 3 months, a rectal thermometer is the most accurate method and the one your pediatrician will want you to use. Forehead (temporal) thermometers work well for babies 3 months and older and are much easier to use. Ear thermometers aren’t considered accurate until after 6 months of age. Armpit readings are the least reliable of all methods, though they can serve as a quick first check. If an armpit reading hits 99°F (37.2°C) or higher in a young infant, follow up with a rectal reading to confirm.
Oral thermometers aren’t practical for babies or toddlers. Save those until your child is at least 4 years old.
Fever-Reducing Medicine by Age and Weight
Acetaminophen (Tylenol) is the only fever reducer recommended for babies under 6 months old, and it should not be used in babies younger than 3 months unless your pediatrician specifically tells you to. Dosing is based on your baby’s weight, not age. Liquid infant acetaminophen comes in a concentration of 160 mg per 5 mL. Here are some common weight ranges:
- 6 to 11 lbs: 1.25 mL
- 12 to 17 lbs: 2.5 mL
- 18 to 23 lbs: 3.75 mL
- 24 to 35 lbs: 5 mL
You can give a dose every 4 to 6 hours as needed, but no more than 5 doses in 24 hours.
Ibuprofen (Motrin, Advil) is not approved for babies under 6 months old. Once your baby is past that mark, ibuprofen becomes another option and can sometimes work better for certain types of discomfort. Always use the measuring syringe that comes with the product rather than a kitchen spoon, which can easily deliver too much or too little.
Keeping Your Baby Comfortable at Home
Dress your baby in one layer of lightweight clothing. It’s tempting to bundle a feverish baby in blankets, especially if they have the chills, but extra layers trap heat and can push the temperature higher. One light blanket for sleep is enough. Keep the room at a comfortable temperature, not overly warm or cold.
A lukewarm bath can help bring some relief. Never use a cold bath, which can actually raise your baby’s internal temperature by triggering shivering. And never apply rubbing alcohol to your baby’s skin. This old home remedy is genuinely dangerous. Rubbing alcohol absorbs through a baby’s skin into the bloodstream and can cause alcohol poisoning, seizures, irregular heartbeat, coma, and even death. The temporary cooling sensation it provides lasts only a minute or two and is not worth the risk.
Fluids and Watching for Dehydration
Fever increases fluid loss, so keeping your baby hydrated is one of the most important things you can do. For babies under 1 year, stick with breast milk, properly mixed formula, or an oral rehydration solution. Don’t give plain water (unless it’s used to make formula), fruit juice, tea, or sugary drinks.
If your baby is vomiting or refusing to feed, try offering small amounts frequently: 1 to 2 teaspoons (5 to 10 mL) of breast milk, formula, or oral rehydration solution every 5 to 10 minutes. This slow approach is easier on the stomach than a full feeding.
Track wet diapers to gauge hydration. A newborn up to 4 months old should have at least 6 wet diapers in a 24-hour period. Fewer than that, especially combined with a dry mouth, no tears when crying, or a sunken soft spot on the head, signals dehydration that needs medical attention.
What to Do During a Febrile Seizure
Some babies and young children have seizures triggered by fever, called febrile seizures. These are frightening to witness but are generally not harmful. Most last less than a couple of minutes. If it happens, note the time it starts and place your baby on the floor on their side to prevent choking. Do not hold them down or restrain them. Do not put anything in their mouth.
If the seizure lasts longer than 5 minutes, call an ambulance. If it stops within 5 minutes but your baby doesn’t seem to recover quickly, also call for help. Any first febrile seizure should be evaluated by a doctor, even if your baby bounces back and seems completely fine afterward.
Red Flags That Need Immediate Attention
Beyond the age-based guidelines above, certain signs mean your baby needs medical care regardless of how high the fever is:
- Listlessness or poor eye contact: A baby who won’t engage with you, seems confused, or is difficult to wake up.
- Signs of dehydration: Fewer wet diapers than usual, no tears, dry mouth, sunken soft spot.
- A rash that doesn’t fade when pressed, especially purple or red spots.
- Difficulty breathing or persistent vomiting.
- A fever that persists beyond 24 hours in a baby under 2 years old without improvement.
On the other hand, if your baby has a mild fever but is still alert, feeding reasonably well, and even playing, the fever itself may not need aggressive treatment. Fever is part of how the immune system fights infection. Sometimes all you need to do is keep your baby comfortable, offer plenty of fluids, and watch for any change in behavior.