If your baby has a fever, the most important first step is knowing their exact age and temperature. A fever is a rectal temperature of 100.4°F (38°C) or higher. For babies under 3 months old, any fever at that threshold needs immediate medical attention, no exceptions. For older babies, most fevers can be safely managed at home while you monitor how your child is acting and feeling.
How to Take an Accurate Temperature
For babies under 3 years old, a rectal thermometer gives the most reliable reading. It’s considered the gold standard by emergency physicians because other methods, like forehead or armpit readings, can miss a true fever or give a falsely high number. Armpit temperatures are the least accurate of all options.
To take a rectal temperature, apply a small amount of petroleum jelly to the tip of a standard digital thermometer and gently insert it about half an inch. Hold it in place until it beeps. If you’ve used a forehead or armpit thermometer first and got a concerning result, follow up with a rectal reading to confirm. Parents naturally prefer less invasive methods, but accuracy matters most when your baby is sick.
When a Fever Needs Emergency Care
Age changes everything with infant fevers. A temperature of 100.4°F in a 2-week-old is treated very differently than the same reading in a 9-month-old. Here’s how to think about urgency:
- Under 3 months old: Any rectal temperature of 100.4°F or higher requires a call to your pediatrician or a visit to the emergency room right away, even if your baby seems fine otherwise. Young infants can have serious infections without showing obvious symptoms.
- 3 to 6 months old: A fever up to 102°F (38.9°C) can often be monitored at home if your baby is feeding, alert, and making wet diapers. Above 102°F, or if your baby seems unusually sleepy or irritable, contact your doctor.
- Over 6 months old: Most fevers are caused by common viral infections and will resolve on their own. Focus on how your baby is behaving rather than the exact number on the thermometer.
Regardless of age, certain symptoms alongside a fever mean you should get help immediately. These include difficulty breathing, skin or lips that look blue, purple, or gray, trouble swallowing (you may notice unusual drooling or spitting), and behavior that seems “off,” like your baby being unusually limp, unresponsive, or withdrawn. Pain or fussiness that keeps getting worse or won’t let up also warrants urgent evaluation.
Fever-Reducing Medication
Acetaminophen (Tylenol) is available in liquid form for infants, typically at a concentration of 160 mg per 5 mL. It can be given every 4 hours as needed, with a maximum of 5 doses in 24 hours. However, it should not be given to babies under 2 months old without your doctor’s guidance. Dosing is based on your baby’s weight, not age, so check the packaging or call your pediatrician’s office if you’re unsure how much to give.
Ibuprofen (Motrin, Advil) is not safe for babies under 6 months old. It hasn’t been proven safe in that age group and isn’t FDA-approved for use before 6 months. Once your baby passes that mark, ibuprofen becomes another option for bringing down a fever and can sometimes work when acetaminophen alone isn’t enough.
Never give aspirin to a baby or child. And always use the measuring syringe that comes with the medication rather than a kitchen spoon, which can easily deliver too much or too little.
Keeping Your Baby Comfortable at Home
A lukewarm sponge bath can help bring a fever down, but it works best when combined with fever-reducing medication. On its own, a bath may cause the temperature to bounce right back up once your baby is out of the water. Use comfortably warm water only. Cold baths, ice packs, and alcohol rubs make things worse by triggering shivering, which actually raises the body’s core temperature.
Dress your baby in light, breathable clothing. It’s natural to want to bundle up a sick baby, but adding extra layers traps heat and can push the fever higher. If your baby’s chest or the back of their neck feels hot or sweaty, remove a layer of clothing or bedding. Their hands and feet will often feel cooler than the rest of their body, and that’s normal. Keep the room between 61°F and 68°F (16 to 20°C), which is the recommended sleep temperature range for babies.
Watch for Dehydration
Fevers increase fluid loss, and babies dehydrate faster than adults. If you’re breastfeeding, offer the breast more frequently. For formula-fed babies, keep to their regular feeding schedule and offer small, frequent feeds if they’re resisting full bottles. Babies over 6 months can also have small sips of water between feeds.
The easiest way to track hydration is by counting wet diapers. A noticeable drop in wet diapers is one of the earliest signs of dehydration. Other warning signs include a sunken soft spot (the fontanelle) on the top of your baby’s head, dry mouth, crying without tears, and unusual drowsiness. If you notice any of these, contact your pediatrician promptly, as young babies can go from mildly dehydrated to seriously dehydrated quickly.
Focus on Behavior, Not Just the Number
A fever of 103°F in a baby who is still playing, drinking, and making eye contact is often less concerning than a fever of 101°F in a baby who is limp and won’t feed. The thermometer tells you part of the story. Your baby’s behavior tells you the rest. Between medication doses, pay attention to whether your child perks up at all. Babies who remain alert and interested in their surroundings during periods when their fever is controlled are generally fighting off a routine illness.
Most fevers in babies older than 3 months resolve within 3 to 5 days. If the fever persists beyond that, or if your baby develops new symptoms like a rash, repeated vomiting, or ear pulling, it’s worth a visit to your pediatrician to check for a secondary infection or other cause that may need specific treatment.