When to get help

Two age thresholds do most of the work here, and they come straight from NICE guideline NG143 on fever in the under-5s.

Under 3 months, 38°C (100.4°F) or higher. NICE says to "recognise that children younger than 3 months with a temperature of 38°C or higher are in a high-risk group for serious illness". This needs assessment now, not in the morning.
3 to 6 months, 39°C (102.2°F) or higher. NICE says these babies are "in at least an intermediate-risk group for serious illness".

Call emergency services immediately — 999 in the UK, 112 or 999 in Ireland and across the EU, 911 in the US and Canada, 000 in Australia, 111 in New Zealand — if your baby has a fever and any of these: a rash that does not fade when you press a glass against it, a stiff neck, a bulging soft spot on the head, a first seizure, unusually cold hands and feet, blue, grey, pale or blotchy skin, lips or tongue, grunting or the stomach sucking in under the ribcage, a weak, high-pitched or continuous cry, or a baby who is drowsy and hard to wake.

Seek urgent same-day advice — NHS 111 in the UK, your GP or GP out-of-hours service in Ireland, your paediatrician in the US or Canada, healthdirect on 1800 022 222 in Australia, Healthline on 0800 611 116 in New Zealand — if either age threshold above is met, if the fever has lasted five days or more, if your baby will not feed, if nappies are drier than usual, or if you are simply worried. NICE is explicit that "reported parental perception of a fever should be considered valid and taken seriously".

What counts as a fever

The NHS defines a high temperature in a child as 38°C (100.4°F) or more, and notes that a normal temperature varies slightly from baby to baby. Most fevers settle within one to four days. The fever itself is not the illness; it is the immune response to one, and in most babies it is doing something useful.

Why babies are treated differently from toddlers

If you have read our page on toddler fever, the advice there was that above six months the number matters far less than the child. That is deliberately not the advice here. NICE draws the line at the same place: recommendation 1.2.11 says that "in children older than 6 months do not use height of body temperature alone to identify those with serious illness". Below six months, and especially below three, the number is doing real diagnostic work, because young babies mount fewer of the obvious signs that make an older child look ill. A three-week-old with a serious bacterial infection can look almost normal.

The NICE traffic light table

NICE publishes a traffic light system for identifying risk of serious illness in the under-5s. Any single sign in the red column puts a child in the high-risk group. Any amber sign with no red sign puts them in the intermediate group. These are the rows, reproduced as NICE writes them.

Red – high risk

Colour: pale, mottled, ashen or blue.
Activity: no response to social cues; appears ill to a healthcare professional; does not wake or if roused does not stay awake; weak, high-pitched or continuous cry.
Respiratory: grunting; tachypnoea — respiratory rate more than 60 breaths per minute; moderate or severe chest indrawing.
Circulation and hydration: reduced skin turgor.
Other: age less than 3 months, temperature more than or equal to 38°C; non-blanching rash; bulging fontanelle; neck stiffness; status epilepticus; focal neurological signs; focal seizures.

Amber – intermediate risk

Colour: pallor reported by parent or carer.
Activity: not responding normally to social cues; no smile; wakes only with prolonged stimulation; decreased activity.
Respiratory: nasal flaring; tachypnoea — more than 50 breaths per minute at age 6 to 12 months, more than 40 at over 12 months; oxygen saturation 95% or less in air; crackles in the chest.
Circulation and hydration: tachycardia — more than 160 beats per minute under 12 months, more than 150 at 12 to 24 months, more than 140 at 2 to 5 years; capillary refill time of 3 seconds or more; dry mucous membranes; poor feeding in infants; reduced urine output.
Other: age 3 to 6 months, temperature more than or equal to 39°C; fever for 5 days or more; rigors; swelling of a limb or joint; non-weight bearing limb or not using an extremity.

Green – low risk

Normal colour; responds normally to social cues; content or smiles; stays awake or awakens quickly; strong normal cry or not crying; normal skin and eyes; moist mucous membranes; none of the amber or red symptoms or signs.

NICE adds one caveat under the table that catches people out at vaccination time: some vaccinations have been found to induce fever in children aged under 3 months.

Taking the temperature

NICE says not to use the oral or rectal routes routinely in children aged 0 to 5. Under 4 weeks, measure with an electronic thermometer in the armpit. From 4 weeks to 5 years, use an electronic or chemical dot thermometer in the armpit, or an infra-red tympanic thermometer. Forehead chemical strips are described as unreliable. The NHS notes that a recent bath, a warm room or heavy wrapping can push a reading up briefly, so wait a few minutes and repeat.

What helps at home

Offer fluids regularly; for a breastfed baby the most appropriate fluid is breast milk. Check on your baby during the night. Do not undress them or sponge them down — NICE does not recommend tepid sponging, and says children with fever should not be underdressed or over-wrapped.

What we are not going to give you

Doses. Paracetamol and ibuprofen suitability depends on your baby's age, weight and country, so read the packaging or ask a pharmacist. What we will pass on is NICE's position on when to use them at all: consider either agent in a child with fever "who appear distressed", but "do not use antipyretic agents with the sole aim of reducing body temperature", and do not give both simultaneously. NICE also states plainly that "antipyretic agents do not prevent febrile convulsions and should not be used specifically for this purpose".

One more trap. NICE warns that when a child has been given antipyretics, you should not rely on whether the temperature falls to tell serious illness from trivial illness. A fever that comes down is not proof of anything.

Fever in Babies