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Fever in babies: what to do and when it is urgent

Creator: OUMM
Published: 2026-10-09

In a baby, age decides most of what you do. Under 3 months, any temperature of 38 °C (100.4 °F) or more is urgent, even if the baby looks well. In an older baby, how they feed, how they look and how many wet nappies they have matter more than the number.

Written by OUMM

Last updated: 9 October 2026

Age decides

Age	Temperature	What to do
under 3 months	≥ 38 °C (100.4 °F)	contact a doctor urgently, also at night; do not wait until morning
3-6 months	≥ 39 °C (102.2 °F)	see a doctor the same day
6-12 months	≥ 38 °C (100.4 °F)	watch how your baby is, feeds and wets nappies; NICE and the NHS: see a doctor for red flags or a fever lasting 5 days or more. This site is more cautious: contact a doctor at ≥ 39 °C or a fever over 3 days (fever in children)

NICE guidance (NG143) puts babies under 3 months with a temperature of 38 °C or more in the high-risk group for serious illness, and babies aged 3-6 months at 39 °C or more in at least the intermediate-risk group. The NHS says to get advice in these age groups also when you think your baby has a high temperature but have no thermometer. In the US, the American Academy of Pediatrics (AAP) asks you to call the pediatrician immediately for a rectal temperature of 100.4 °F (38 °C) or more under 3 months, and for 3-6 month olds already from 101 °F (38.3 °C): follow your own doctor's advice. For older children, see fever in children.

Check the temperature and age

How to take a baby's temperature

Under 4 weeks: NICE recommends an electronic thermometer in the armpit.
From 4 weeks: an electronic or chemical dot thermometer in the armpit, or an infra-red ear thermometer.
Armpit, step by step (NHS): place the tip high in the armpit, gently hold the arm against the body and keep it there as long as the thermometer's instructions say.
Just after a bath or a blanket the reading can be high for a short time: wait a few minutes and measure again.

NICE advises against routine mouth or rectal readings in children under 5. The AAP considers a rectal reading the most accurate in babies, especially under 3 months, and advises against ear thermometers under 6 months. Whichever you use, stick to one method and log it with each reading. More in how to take a child's temperature.

Feeding and fluids

What matters most is that your baby keeps feeding. NICE and the NHS: offer fluids regularly, and if you breastfeed, carry on as normal: breast milk is the best fluid for a breastfed baby. Shorter, more frequent feeds are fine. Do not undress your baby or sponge them down to cool them, and do not bundle them in lots of clothes or blankets either (NICE, NHS).

Dehydration: what to look for

Babies dehydrate faster than older children. Signs from NICE, the NHS and the AAP:

fewer wet nappies (diapers) than usual or nappies that are hardly wet (AAP: in infants, fewer than six wet diapers a day),
a sunken soft spot (fontanelle) on the head,
a dry mouth, sunken eyes, few or no tears when crying,
drowsy or irritable, not interested in feeding.

Any of these is a reason to contact a doctor. Dehydration also matters for medicines: ibuprofen leaflets warn of kidney problems in dehydrated children, and the NHS says not to give ibuprofen to a child who is dehydrated.

Fever medicines in babies: from what age

Medicine is for a baby who is distressed (crying, cannot be settled, not feeding), not for chasing the number on the thermometer (NICE). It does not prevent febrile seizures. Age limits come from the product leaflets:

Under 3 months: paracetamol (acetaminophen) only on a doctor's recommendation; no ibuprofen. The NHS says: "do not give paracetamol to a child under 2 months". At this age a fever means calling a doctor first, not reaching for medicine.
Ibuprofen: as a rule from 3 months and 5 kg; MIG dla dzieci from 6 months; Ibum, Ibufen, Ibuprom: under 6 months only after consulting a doctor. In babies aged 3-5 months, see a doctor if symptoms worsen or do not settle after 24 hours.
Paracetamol: limits depend on the product (for example Paracetamol Hasco and suppositories: under 2 years on a doctor's order).

Doses in millilitres, intervals and the full list of leaflet age limits are on paracetamol dose for children and ibuprofen dose for children. To compare the two: paracetamol or ibuprofen.

Red flags: call emergency services

Whatever the temperature and age (NHS, NICE):

a rash that does not fade when you press a glass against it,
a bulging fontanelle, a stiff neck, bothered by light,
difficulty breathing: grunting, the tummy sucking in under the ribs, breathing very fast,
pale, grey, blue or blotchy skin, lips or tongue; unusually cold hands and feet,
hard to wake, floppy, not responding as usual, not interested in feeding,
a weak, high-pitched or continuous cry,
a fit (seizure), especially the first one.

The full list by age: when to see a doctor with a child's fever.

Fever after vaccinations

NICE notes that some vaccinations can cause fever in babies under 3 months. The rule does not change: a baby under 3 months at 38 °C or more needs a doctor; tell them which vaccine was given and when. What is typical after vaccines in older babies is covered in fever after vaccination.

Common questions

Is 37.5 °C a fever in a newborn?

No. The NHS and NICE count 38 °C (100.4 °F) or more as a fever. But if a newborn is drowsy, feeding poorly or just does not seem right, contact a doctor whatever the number.

Can I wait until morning with a 2 month old at 38 °C?

No. Under 3 months this is urgent, at night too and even if the baby seems fine. Call your doctor's out-of-hours service (NHS 111 in the UK) or, in an emergency, 999 or 911.

The temperature came down after medicine, so it is nothing serious?

You cannot tell that way. NICE: whether the temperature drops after medicine does not separate serious from mild illness. Look at your baby: how they respond, whether they feed, whether nappies are wet.

Should I stop breastfeeding during a fever?

No. The NHS and NICE say to carry on, and breast milk is the best fluid for a feverish breastfed baby.

Check the official source

These numbers are conversions from leaflets and guidelines. Before giving a medicine, confirm them at the source:

NHS: paracetamol for children · NHS: ibuprofen for children
NICE NG143: fever in under 5s · AAP HealthyChildren.org
Polish medicines register (URPL): official leaflets of the products listed here
Leaflets in the Polish register: Apap dla dzieci Forte (40 mg/ml) · Paracetamol Hasco (120 mg/5 ml) · Panadol dla dzieci (120 mg/5 ml) · Pedicetamol (100 mg/ml) · Czopki 125 mg (125 mg) · Czopki 250 mg (250 mg) · Czopki 500 mg (500 mg) · Nurofen dla dzieci Forte (200 mg/5 ml) · Ibum (100 mg/5 ml) · Ibum Forte (200 mg/5 ml) · Ibufen dla dzieci (100 mg/5 ml) · Ibufen dla dzieci Forte (200 mg/5 ml) · Ibuprom dla dzieci Forte (40 mg/ml) · MIG dla dzieci (20 mg/ml) · MIG dla dzieci Forte (40 mg/ml) · Nurofen czopki 60 mg (60 mg) · Nurofen czopki 125 mg (125 mg)
Dosing sources: every leaflet table as the calculator and the Android app encode it, the leaflet date, the register link and every added rule, with its reason
Your own country's medicines regulator and the leaflet in the box always take precedence.

Tired of keeping track on a scrap of paper?
Oh Fever records what you gave and when. Free for one child.

iPhone and Apple Watch

Shows the time since the last dose, the doses recorded in 24 hours and the leaflet tables and sentences word for word, with a link to the official leaflet. It does not calculate or suggest doses.

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Android

Also shows the row of the leaflet table for your child's weight and age, counts down to the next dose the leaflet allows and warns before the daily limit is crossed.

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