Baby fever: what temperature is too high, and when to worry
Fever is one of the most common reasons parents call a doctor, and usually a sign the immune system is doing its job. Age matters more than the number. Here's how to measure it properly, what's normal after vaccines, and the signs that mean go now.
A fever in a baby is a temperature of 38°C (100.4°F) or higher. Any fever in a baby under 3 months needs a doctor the same day, and a temperature of 39°C or more at 3–6 months needs a call to your paediatrician. At any age, go urgently for breathing difficulty, a rash that doesn't fade when pressed with a glass, unusual floppiness or drowsiness, a seizure, signs of dehydration, or a fever lasting five days or more. How your baby looks and behaves matters more than the exact number.
A fever is not an illness. It's the body raising its thermostat to fight an infection, and in most babies over three months it comes from a virus that will pass on its own. The job is to work out whether this is one of those — or one of the less common cases that needs a doctor now.
What counts as a fever
A normal temperature for a baby is about 36.5–37.5°C (97.7–99.5°F). A fever is 38°C (100.4°F) or higher. A slightly raised reading after a bath, a feed or being bundled up is not a fever — wait fifteen minutes in lighter clothes and re-check.
How to take your baby's temperature
- Use a digital thermometer. Mercury thermometers are a poisoning risk if they break; strip and forehead-sticker thermometers aren't reliable.
- Under 5 years: the armpit is the standard method in the UK's NICE guidance — tip in the armpit, arm held gently against the side. For young infants, the AAP considers a rectal reading most accurate; ask your paediatrician which they prefer.
- Ear and infrared forehead thermometers are fine for older babies if used exactly as the instructions say.
- Write down the reading and the time. Your doctor will ask how high and for how long.
When to see a doctor, by age
| Age | Temperature | What to do |
|---|---|---|
| Under 3 months | 38°C or higher | See a doctor the same day, even if the baby seems well. Young babies can be seriously unwell with few other signs. |
| 3–6 months | 39°C or higher | Call your paediatrician today. |
| Any age | Any fever lasting 5 days or more | See a doctor. |
| Any age | Any fever with a red flag below | Go to hospital now. |
Red flags: go now
is struggling to breathe, grunting, or the skin between the ribs sucks in · has blue, grey or very pale lips or skin · is floppy, very drowsy or hard to wake · has a weak, high-pitched or continuous cry · has a rash that doesn't fade when you press a glass against it · has a bulging soft spot · has a fit (seizure) · has no wet nappy for 12 hours or won't feed · has green vomit.
What you can do at home
- Keep feeding. Offer breast or bottle more often — fever increases fluid needs.
- Don't overwrap. Light clothing and a normal room temperature. Heavy blankets trap heat.
- Skip cold sponging. It makes babies shiver and doesn't help; tepid sponging isn't recommended either.
- Paracetamol can make a baby more comfortable if they are distressed — the goal is comfort, not a normal number. Dose it by your baby's weight as your paediatrician advises, and check the concentration: drops and syrups are different strengths. Don't give paracetamol under 2 months without a doctor's advice.
- Ibuprofen is not for babies under 3 months, or if they are dehydrated. In India, during dengue season, avoid ibuprofen until your doctor has ruled dengue out.
- Log it. Temperature, time, any medicine and dose, feeds and wet nappies. That's what your doctor will ask for.
Fever after vaccines
A mild fever within 24–48 hours of a vaccine is common and usually settles within a day or two — it's more common after the whole-cell pertussis (DTwP) vaccine than the acellular one. The MMR vaccine can cause a fever and sometimes a faint rash 7–12 days later. A fever above 39°C, one lasting more than 48 hours, or any fever with red flags isn't something to put down to the vaccine — call your doctor. See our IAP vaccination chart for when each dose falls.
Teething doesn't cause high fever
Teething can nudge the temperature up slightly, but it doesn't cause a fever of 38°C or more. If your baby has a real fever, look for another cause. More in our teething guide.
Keeping track
When your baby is ill, the details blur fast. Araia lets you log temperatures, symptoms and medicines with the time, so you can see at a glance when the last dose of paracetamol was — and hand your paediatrician a clear timeline, or share it through the clinician portal.
Frequently asked questions
What temperature is a fever in a baby?
When should I worry about my baby's fever?
Is fever normal after vaccination?
Does teething cause fever?
Should I give paracetamol for every fever?
This guide is general information for Indian parents, written from published paediatric guidance (IAP, WHO, AAP). It is not medical advice and cannot account for your baby specifically. Anything that worries you — feeding, breathing, fever, weight, a rash — is a call to your paediatrician, not a search. In an emergency, go to a hospital.
Stop keeping it all in your head
Araia logs feeds, nappies, sleep and weight in one tap, tracks the IAP vaccination schedule for you, and answers questions using your own baby's history.