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

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

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.

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.