Baby Fever: When to Worry and When to Call the Doctor
A fever in a baby can be frightening. Learn what temperature counts as a fever, how to treat it at home, and the specific warning signs that require urgent medical attention.
Medical Information
The information on this page is for educational and informational purposes only. It is not medical advice and should not be used to diagnose or treat any medical condition. Always consult your healthcare provider (doctor, midwife, or nurse) before making any decisions about your pregnancy or your baby's health.
What Is a Fever?
A fever is a body temperature of 38°C (100.4°F) or above. It is usually the body's natural immune response to infection — a sign that the immune system is working.
A single temperature reading above normal does not automatically mean something is seriously wrong. However, in young babies, fever always warrants attention because their immune systems are still developing and they can deteriorate quickly.
Fever by Age: Urgency Guide
Under 3 Months — Seek Emergency Care Immediately
Any fever of 38°C or above in a baby under 3 months is a medical emergency. Call your GP urgently or go to A&E. Do not wait.
Young babies cannot fight infection as effectively as older children, and what seems like a mild illness can become serious very quickly.
3–6 Months — Call Your Doctor Same Day
A temperature of 38°C or above warrants a same-day call to your GP or a visit to an urgent care centre, particularly if your baby:
- Is not feeding well
- Is unusually sleepy or difficult to rouse
- Has a rash
- Has been crying continuously
6 Months and Older — Monitor and Assess
A fever in a baby over 6 months can often be managed at home if your child is drinking fluids, can be comforted, and has no alarming symptoms (see below). If in doubt, always call your doctor.
Warning Signs That Always Require Urgent Care
Regardless of age, seek immediate medical attention if your baby has a fever AND any of the following:
- 🚨 Stiff neck or sensitivity to light
- 🚨 Rash that doesn't fade when pressed (glass test)
- 🚨 Difficulty breathing or fast, laboured breathing
- 🚨 Lips or fingernails turning blue or pale
- 🚨 Unresponsive or unusually limp — difficult to rouse
- 🚨 Persistent crying that is not consolable
- 🚨 Bulging fontanelle (the soft spot on the head)
- 🚨 First febrile seizure (fitting)
- 🚨 Fever above 40°C at any age
How to Take a Baby's Temperature
Digital rectal thermometer (under 3 months — most accurate)- Use a small amount of petroleum jelly on the tip
- Insert 1–2cm and hold for 1 minute
- Normal rectal temperature: 36.6–38°C
- Swipe across the forehead
- Quick and convenient for home monitoring
- Hold the thermometer snugly under the armpit for the required time
- Add 0.3–0.5°C to the reading for accuracy
Managing Fever at Home (Over 3 Months)
Fever-reducing medicines:- Infant paracetamol (Calpol) — from 2 months (if over 4kg and not premature)
- Infant ibuprofen — from 3 months (not for babies under 5kg)
- Never exceed the recommended dose or give both at the same time unless a doctor advises otherwise
- Dress in light clothing — do not over-bundle
- Keep the room comfortably cool
- Offer frequent feeds — breast milk or formula for babies, water for babies over 6 months
- Skin-to-skin can be calming during mild fevers
- Use cold baths or cold compresses — these cause shivering, which raises body temperature
- Give aspirin — never give aspirin to children under 16
Common Causes of Fever in Babies
- Viral respiratory infections (common cold, flu)
- Ear infections
- Urinary tract infection (UTI) — more common than many parents realise
- Roseola (6–24 months) — high fever followed by a distinctive rash
- Post-vaccination fever (usually mild and short-lived, within 48 hours of vaccination)
A cause isn't always immediately obvious — your doctor will examine your baby thoroughly to identify it.
Keeping Records
When you speak to your doctor, they will want to know:
- Your baby's temperature and when it started
- How long the fever has lasted
- Other symptoms (cough, rash, feeding changes, nappy output)
- Any medicines given and when
- Recent vaccinations
A quick note in your phone when you first notice the fever saves valuable time.
Frequently Asked Questions
What temperature is a fever in a baby?
A temperature of 38°C (100.4°F) or above is considered a fever in a baby. Anything above 38°C in a baby under 3 months requires immediate medical attention.
What is the most accurate way to take a baby's temperature?
A digital rectal thermometer gives the most accurate reading in babies under 3 months. For older babies, a temporal (forehead) or axillary (armpit) thermometer is convenient and reliable enough for home use.
Does teething cause fever?
Teething may cause a very slight temperature rise (below 38°C), but it does not cause a true fever. If your teething baby has a temperature of 38°C or above, look for another cause and contact your doctor.
PregnancySprout Editorial Team
Our editorial team researches every article against primary medical sources — NHS, WHO, NICE, and RCOG guidelines. We are health writers and parents, not doctors; content is reviewed for accuracy but does not constitute medical advice.
✓ Fact-checked against NHS, WHO, and NICE guidelines