Baby Fever: Temperature Guide, When to Call the GP & When to Go to A&E

Baby fevers are almost inevitable in the first year — especially once nursery or older siblings enter the picture. Knowing when to treat at home, when to call the GP, and when to go straight to A&E could genuinely be the difference between a worried night and a medical emergency.

What is a normal baby temperature?

Normal: 36.4°C (but anywhere from 36.0–37.0°C is fine)
Low-grade fever: 37.1–37.9°C
Fever: 38.0°C or above
High fever: 39.0°C or above

How to take baby's temperature

Digital axillary (armpit) thermometer — the safest and most practical for babies. Place under the arm, hold arm snugly against body for 60 seconds. Add 0.5°C to get the approximate core temperature.

In-ear (tympanic) thermometer — fast and reasonably accurate from 6 months+ but less reliable in babies under 6 months due to ear canal size.

Forehead (temporal) thermometer — convenient but least accurate; useful for quick checks, not diagnosis.

Rectal thermometer — gold standard for accuracy but not recommended for home use in babies without training.

Never use: Mercury thermometers (they're banned in the UK) or mouth thermometers for babies.

What causes fever in babies?

Fever is the body's healthy immune response — it means the immune system is working. Common causes:

• Viral infections: Colds, flu, roseola, hand foot and mouth disease, chickenpox
• Bacterial infections: Ear infections, throat infections, urinary tract infections (UTIs), pneumonia
• Immunisations: A mild fever for 1–2 days after vaccinations is normal and harmless
• Overheating: Remove layers before rechecking — an overdressed baby can have an elevated temperature that isn't illness

Managing fever at home

When temperature is 38.0–39.5°C in a baby over 3 months:

1. Remove excess clothing — dress in light layers
2. Keep room cool — 18–20°C
3. Offer fluids frequently — breastmilk, formula, or water (if over 6 months) to prevent dehydration
4. Paracetamol (Calpol) for babies 2 months+ if they're distressed or uncomfortable — dose by weight, not age. Ibuprofen from 3 months+.
5. Don't alternate paracetamol and ibuprofen unless GP advised — pick whichever helps and use correctly
6. Monitor closely — check temperature every hour or two

Things NOT to do:

• Don't undress baby and sponge with cool water — this is no longer recommended (can cause shivering which raises temperature)
• Don't overdress in an attempt to "sweat it out"
• Don't give aspirin to under 16s

When to call NHS 111

Call 111 if:

• Baby is under 3 months with any fever above 38°C
• Baby is 3–6 months with fever above 39°C
• Fever doesn't respond to paracetamol/ibuprofen
• Fever lasting more than 5 days
• Baby is not taking fluids / signs of dehydration (dry nappies, sunken fontanelle, dry mouth)
• You're worried for any reason — 111 is there to help you decide

When to call 999 or go to A&E immediately

Red flag symptoms — don't wait:

• Non-blanching rash — small dark red or purple spots (petechiae) that don't fade when pressed with a clear glass. Could be meningococcal disease. Call 999 immediately.
• Difficulty breathing — rapid breathing, flaring nostrils, ribs visible when breathing (recession), grunting
• Seizure (febrile convulsion) — rhythmic jerking, stiffness, loss of consciousness. Call 999. Febrile convulsions are frightening but rarely dangerous; get medical help.
• Bulging fontanelle (soft spot on head feels tight/raised when baby is calm and upright)
• High-pitched or unusual cry
• Extremely pale, blotchy, or mottled skin
• Cold hands and feet with a hot trunk (sign of circulatory compromise)
• Lethargic — unresponsive, difficult to rouse
• Any fever in a baby under 3 months if you can't speak to a clinician quickly

The meningitis glass test

Hold a clear glass firmly against a rash. If spots fade under pressure — blanch — they are unlikely to be meningococcal. If they don't fade — stay dark through the glass — call 999 immediately. Don't wait for more spots to appear.

After the fever

Most fevers from viral infections resolve within 3–5 days. A day or two of being clingy and off food after a fever is normal. If the fever returns after a clear 24-hour break, or if baby develops new symptoms, call your GP.

Immunisations and fever

A mild fever (37.5–38.5°C) for up to 48 hours after immunisations is normal and expected. Give paracetamol if baby is distressed. The exception: the MenB vaccine at 8 weeks is associated with higher fevers — your vaccination nurse will advise you to give paracetamol before and after this specific vaccination.

Trust your instincts

You know your baby better than anyone. If something feels wrong — if they just don't seem right even without a high temperature — trust that instinct and call NHS 111. You will never be wasting their time.