Fever in babies: what to do at every age — and the under-3-months rule

The rule that comes before everything

If your baby is younger than three months and has a temperature of 38°C (100.4°F) or more, go to the hospital the same day. Not tomorrow, not after a sponge bath, not after asking the family group. This is the single most important sentence in this article, and it has no exceptions.

Why so absolute? A newborn's immune system cannot yet wall off infections — a bug that would give an older child a runny nose can spread through a newborn's body in hours, and fever is often the only visible sign. Doctors do not 'wait and watch' newborn fever, and neither should any household.

This is also why the temperature must be measured, not felt. A hand on the forehead detects warmth, not numbers. Every home with a baby needs a thermometer — a basic digital one from any chemist is enough, used in the armpit.

What counts as fever

38°C (100.4°F) and above, measured in the armpit, is fever. 37.5-38°C is borderline — recheck after 30 minutes, with the baby unwrapped from heavy layers (overdressing alone can raise a small baby's reading).

The number matters less than the age and the behaviour. A 6-month-old at 38.5°C who is feeding, smiling and playing is a different situation from the same number in a baby who is limp, refusing feeds or hard to wake — the second set goes to the doctor regardless of what the thermometer says.

Fever itself is not the illness — it is the body fighting one. The job at home is comfort and fluids, spotting the danger signs, and knowing which situations skip home care entirely.

Home care that actually helps

Feed more, not less — breastmilk or formula is both food and fluid, and fever spends water fast. Offer feeds frequently; for babies over six months, water and normal food as accepted.

Dress light. The instinct to bundle a feverish baby in blankets is exactly backwards — one light layer in a normally ventilated room lets heat escape. No cold-water baths and no ice — they cause shivering, which raises temperature.

Paracetamol in the correct dose for the baby's weight is the standard fever medicine — but the dose must come from your doctor or the label's weight chart, never from memory or a neighbour. Never give aspirin to a child, and do not combine multiple fever syrups.

What does not help: rubbing alcohol, onion in the socks, starving the fever, antibiotic drops left over from last time. Antibiotics treat bacteria on prescription, not fever on demand — most childhood fevers are viral and antibiotics do nothing for them.

The danger signs, by age

Go the same day, at any age, if fever comes with any of these: refusing feeds or not passing urine for 6-8 hours; unusually sleepy, limp or hard to wake; fast or laboured breathing, or the chest sucking in with each breath; a fit (convulsion); a rash that does not fade when pressed; continuous inconsolable crying; vomiting everything; or a soft spot on the head that bulges.

Under 3 months: any fever at all — same-day hospital, as above. 3-6 months: fever of 39°C or more, or any fever lasting beyond 24 hours, sees a doctor. Over 6 months: fever beyond 3 days, or any of the danger signs above, sees a doctor.

For emergencies, 108 is the free national ambulance number. The ASHA worker's home-based newborn care visits (days 3, 7, 14, 21, 28 and 42) exist exactly to catch newborn danger signs — take them seriously and show her the baby.

Fever after vaccination

Mild fever in the 24-48 hours after a vaccine dose is common and expected — the immune system is doing its work. Comfort, fluids and doctor-approved paracetamol are enough; the fever passes in a day or two.

The under-3-months rule has one nuance here: if the fever arrives within 48 hours of a vaccination and the baby is otherwise feeding and behaving normally, phone your doctor and describe it — many will guide you at home. Any fever outside that window, or any of the danger signs, follows the main rule: same day, in person.

Never skip the next vaccine dose because the last one caused fever — tell the doctor, who will advise. The diseases the schedule prevents are far worse than a day of post-vaccine warmth.

When to see a doctor at once

Under 3 months with any fever: same-day hospital. Any age: danger signs listed above — same day. Fever with stiff neck, a first convulsion, or a non-fading rash: emergency, 108 if needed.

This article is general information, not medical advice, and is no substitute for personal medical advice. For any decision about your or your child's health, please consult your doctor.

Frequently asked questions

Q: The fever touches 40°C at night — does a higher number mean a more serious illness? — Not by itself; some minor viral fevers run high and some serious illnesses run low-grade. Behaviour beats the number: alert and feeding is reassuring at 39.5°C; limp and refusing feeds is alarming at 38°C. High fever that won't settle with medicine, though, deserves a same-day review.

Q: My baby had a fit with fever — will it happen again? Is it epilepsy? — Febrile convulsions happen in a small percentage of children between 6 months and 5 years, look terrifying, and usually cause no lasting harm. Any first fit needs same-day hospital assessment to rule out other causes. A single febrile fit is not epilepsy; your doctor will explain what to do if one recurs.

Q: Should I alternate paracetamol and ibuprofen like the internet says? — Not on your own. Alternating schedules exist but dosing errors are the commonest medicine accident in children — use one medicine, at the weight-correct dose, at the correct interval, and let the doctor decide if more is needed.

Q: Grandmother says teething causes fever — true? — Teething can make gums sore and babies cranky and drooly, and may nudge the temperature slightly — but it does not cause true fever (38°C+). Blaming a real fever on teething is how infections get missed; a 38°C+ reading follows the fever rules regardless of teeth.