Baby Fever: What Is Normal, What to Do, and When to Worry

Few things make a parent's stomach drop like a hot little forehead. A fever can be frightening, but here is the reframe that helps: a fever is not an illness — it is the body doing its job, raising its temperature to fight off an infection. What matters most is not the exact number, but your baby's age and how they seem. Here is what is normal, how to respond, and the clear signs that mean call the doctor now.

What counts as a fever?

A fever is a body temperature of 100.4°F (38°C) or higher. Below that is not a fever. A baby's normal temperature can vary a little through the day and with activity, so a reading slightly above their usual — but under 100.4°F — is not a fever.

Crucially, how high the fever is does not reliably tell you how serious the illness is. A high fever can come with a mild virus, and a serious illness can come with only a modest one. So watch your baby, not just the thermometer.

How to take your baby's temperature accurately

For babies, accuracy matters:

• Under 3 months: a rectal temperature is the most accurate and the one doctors rely on. It sounds daunting but is safe when done gently with a digital thermometer.
• Older babies: rectal is still most accurate; forehead (temporal) and armpit readings are easier and fine for a general sense, though less precise.
• Avoid old mercury thermometers and, for young babies, ear thermometers (less reliable under 6 months).
• Note the time and the number, and which method you used, so you can tell the doctor.

What to do by age

This is the part that matters most — the response depends heavily on age.

Under 3 months is the critical one: any fever of 100.4°F (38°C) or higher in a baby under three months is treated as a potential emergency, because young infants can get seriously ill quickly and show few other signs. Call your doctor or go to the emergency department right away — do not wait, and do not give fever medicine before speaking to a professional.

For older babies, a fever with an otherwise okay-seeming baby can often be managed at home with comfort and monitoring — but always trust your instinct and call if something feels off.

How to comfort a feverish baby

For a baby old enough to manage at home (and with your doctor's okay):

• Keep them comfortable and hydrated. Offer extra breast milk or formula; hydration matters more than food. Watch for wet diapers.
• Dress them lightly — one light layer. Bundling traps heat and raises the temperature. Keep the room comfortable, not hot.
• Rest. Let them sleep and take it easy.
• Fever medicine, correctly. For babies over the appropriate age, infant acetaminophen (and ibuprofen for babies over 6 months) can ease discomfort — but dose strictly by weight and your pediatrician's guidance, never by age alone, and never give aspirin to a child. Only medicate to help them feel better, not to force the number down.
• Skip cold baths, ice, and alcohol rubs — they can cause shivering (which raises temperature) and are not recommended.

Febrile seizures: frightening but usually harmless

One thing worth understanding *before* it happens, because it is terrifying in the moment: some young children have a febrile seizure — a convulsion triggered by a fever, most common between about 6 months and 5 years. The child may stiffen, twitch or jerk, and briefly lose awareness. It is one of the scariest things a parent can witness, but the reassuring truth is that most febrile seizures are brief and harmless, and do not cause brain damage or mean your child has epilepsy. If one happens: stay as calm as you can, place your baby on their side on a safe surface away from hard objects, do not put anything in their mouth or restrain them, and time it. For a first-ever seizure, a seizure lasting more than about 5 minutes, or one with trouble breathing or a blue color, call emergency services immediately. Even for a short one that stops on its own, contact your doctor afterward to check in. Knowing this exists — and that it usually passes without harm — makes it far less frightening if you ever face it.

When to call the doctor or seek urgent care

Call your doctor promptly — or seek emergency care — for any of these:

• Any fever in a baby under 3 months (100.4°F / 38°C or higher)
• A fever in a 3–6 month old, or a fever above about 102°F (39°C) in an older baby
• Fever lasting more than a couple of days, or that keeps returning
• Your baby is hard to wake, floppy, or unusually unresponsive
• Trouble breathing, a blue tinge to lips or skin
• A rash that does not fade when pressed (glass test) — seek emergency care
• Repeated vomiting, signs of dehydration (few wet diapers, no tears, dry mouth), or a stiff neck
• A febrile seizure (stay calm, keep them safe on their side, and seek medical advice)
• Your baby simply seems very unwell, or your gut says something is wrong — trust it

Frequently asked questions

What temperature is a fever in a baby?

100.4°F (38°C) or higher is a fever. Below that is not. Remember the height of the fever does not reliably indicate how serious the illness is — your baby's age and how they seem matter more.

My baby is under 3 months and has a fever — what do I do?

Treat it as urgent. Any fever of 100.4°F (38°C) or higher in a baby under three months means calling your doctor or going to the emergency department right away, without giving fever medicine first. Young infants can become seriously ill quickly.

How do I take my baby's temperature?

A rectal reading with a digital thermometer is the most accurate for babies, especially under three months. Forehead and armpit readings are easier for older babies but less precise. Avoid ear thermometers under six months.

Should I give my feverish baby medicine?

Only to ease discomfort, for a baby old enough, dosed by weight and your pediatrician's guidance — never by age alone, and never aspirin. For babies under three months, speak to a doctor before giving anything.

The takeaway

A fever (100.4°F/38°C or higher) is the body fighting infection, and your response depends above all on age: any fever under 3 months is an emergency — call right away; older babies can often be comforted and monitored at home with fluids, light clothing and correctly-dosed medicine if needed. Watch your baby rather than the number, know the red flags, and always trust your instinct. And keep the whole thing in perspective: fevers are one of the most common and normal parts of a baby getting sick, most are caused by ordinary viruses that pass on their own, and a child who is drinking, weeing and settling reasonably between temperature spikes is usually okay — the thermometer reading matters far less than how they seem. For related illness, see our guide to baby's first cold.

*This article is general information, not medical advice. For any fever in a baby under 3 months, or any concern, contact a medical professional immediately.*