Fever in Babies: When to Worry and When to Call the GP

6 min read

Quick answer: A temperature of 38°C or above counts as a fever in babies. Under 3 months, that is always a medical emergency: call 999 or go to A&E. At 3 to 6 months, call 999 or go to A&E at 39°C or higher, unless they had a vaccine in the past 2 days. From 3 months, call 111 or ask for an urgent GP appointment if a fever lasts more than 5 days, or if you are worried.

What parents need to know

Your baby feels warm. You grab the thermometer. The reading says 38.2°C. What do you do? For many new parents, this scenario triggers immediate panic. But once you understand what a fever means, when it matters, and what to watch for, you'll feel far more confident managing it.

What temperature is a fever in babies?

According to NHS guidance:

A temperature of 38°C or above is considered a fever in babies and children.
In babies under 3 months, a temperature of 38°C or above is always a medical emergency: call 999 or go to A&E.
In babies 3 to 6 months, a temperature of 39°C or higher means call 999 or go to A&E, as long as they have not had a vaccine in the past 2 days.

How to take your baby's temperature accurately

The most reliable method for babies under 5 years is a digital thermometer in the armpit (axillary temperature). Place the thermometer snugly in the armpit and hold the arm gently against the body for the required time (check your thermometer's instructions, usually about 15 seconds).

Ear thermometers can be less accurate in young babies due to small ear canal size. Forehead strip thermometers are not accurate enough to rely on for medical decisions.

Normal body temperature is around 36.4°C, though there is natural variation between children and throughout the day.

What causes fever in babies?

A fever is not a disease itself — it's the body's immune response to infection. Common causes include:

Viral infections (colds, flu, roseola, hand foot and mouth)
Ear infections
Urinary tract infections (UTIs), common and often without obvious symptoms in babies
Bacterial infections (less common but more serious)
Post-immunisation fever (normal and expected, usually mild and short-lived)

Teething does not cause a true fever of 38°C or above. If your baby has a high temperature, investigate further.

What to do when your baby has a fever

Keep them comfortable

Dress them in light clothing. Don't bundle them up
Keep the room at a comfortable temperature
Offer plenty of fluids — breast milk, formula, or water for babies over 6 months
Don't rely on fans or cold flannels to cool them — these can cause shivering which raises temperature

Use infant paracetamol or ibuprofen

Age-appropriate liquid paracetamol (from 2 months, if over 4kg and born after 37 weeks of pregnancy) can help reduce fever and ease discomfort. Infant ibuprofen is suitable from 3 months (over 5kg). Do not give both at the same time, and do not alternate them unless a health professional such as a doctor or nurse tells you to.

Never give aspirin to a child under 16.

Warning signs: call 999 or go to A&E

Call 999 or go to A&E immediately if your baby:

Has a non-blanching rash (doesn't fade when pressed with a glass) — this could indicate meningitis
Has a temperature of 38°C or above and is under 3 months old
Has a temperature of 39°C or higher and is 3 to 6 months old (and has not had a vaccine in the past 2 days)
Has a very low temperature (less than 36°C), or feels cold to touch or is shivery
Has a seizure (febrile convulsion)
Is difficult to rouse or unusually drowsy
Has a weak, high-pitched or continuous cry
Has a bulging fontanelle (the soft spot on the top of the head)
Has blue, grey, paler than usual or blotchy skin, lips or tongue (this may be harder to see on brown or black skin)
Has a stiff neck
Seems to be in extreme pain
Is bothered by light
Has unusually cold hands and feet
Is extremely agitated (does not stop crying) or is confused
Has difficulty breathing (you may notice grunting noises or their tummy sucking in under their ribs), is breathless or is breathing very fast
Is not responding like they normally do, or is not interested in feeding or normal activities
Has not had a pee or a wet nappy in the past 12 hours

Call 111 or your GP if

Your baby is 3 months or older and has had a temperature of 38°C or higher for more than 5 days
They have other signs of illness, such as a rash, as well as a high temperature
They do not want to eat, or are not their usual self and you are worried
They seem dehydrated, for example nappies that are not very wet, sunken eyes, and no tears when they cry
You are worried for any reason — parental instinct matters

Post-immunisation fever

A mild fever after vaccinations is normal and a sign the immune system is responding. It usually appears within 24 hours and resolves within 48 hours. Infant paracetamol can help. If your baby is under 3 months old and has a temperature of 38°C or higher, call 999 or go to A&E. Otherwise, if the fever is high (38°C or higher), persistent, or accompanied by other symptoms, contact 111.

Frequently asked questions

What is the most accurate way to take a baby's temperature?

For babies under 5 years, use a digital thermometer in the armpit, holding the arm gently against the body for the time your thermometer states, usually about 15 seconds. Ear thermometers can be less accurate in young babies, and forehead strips are not reliable.

Can teething cause a fever in babies?

No. Teething does not cause a true fever of 38°C or above, so if your baby has a high temperature you should investigate further rather than assuming it is teeth.

When can I give my baby paracetamol or ibuprofen for a fever?

Age-appropriate liquid paracetamol can be given from 2 months if your baby is over 4kg and was born after 37 weeks of pregnancy, and infant ibuprofen from 3 months if over 5kg. Do not give both at once, and never give aspirin to a child under 16.

Is a fever after vaccinations normal?

Yes. A mild fever after vaccinations is normal and shows the immune system is responding. It usually appears within 24 hours and settles within 48. If your baby is under 3 months old and has a temperature of 38°C or higher, call 999 or go to A&E. Otherwise, contact 111 if it is high, persistent or comes with other symptoms.

Sources & further reading

General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.