Baby Fever: When to Worry and When to Call the Doctor

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, not failing.

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: The 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. Do not wait to see if it comes down. Call your GP urgently or go to A&E immediately.

Young babies cannot fight infection as effectively as older children. What seems like a mild fever can mask a serious bacterial infection (such as meningitis, sepsis, or urinary tract infection) that can become life-threatening within hours. This age group is treated as urgent regardless of other symptoms.

3–6 Months — Call Your Doctor Same Day

A temperature of 38°C or above warrants a same-day call to your GP or an urgent care visit, particularly if your baby:

• Is not feeding well or has had significantly fewer wet nappies than normal
• Is unusually sleepy or difficult to rouse
• Has a rash anywhere on the body
• Has been crying continuously for more than 2 hours

If you cannot reach your GP, call NHS 111 or go to an urgent care centre.

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. However, if in doubt, always call your doctor or NHS 111.

Warning Signs That Always Require Emergency Care

Regardless of age or temperature, go to A&E or call 999 immediately if your baby has a fever AND any of the following:

• 🚨 Stiff neck — unable to put their chin to their chest, or cries when their neck is moved
• 🚨 Sensitivity to light — turns away from or cries at normal light
• 🚨 Rash that doesn't fade when pressed with a glass or a clear cup (the glass test) — press firmly for 10 seconds
• 🚨 Difficulty breathing — fast, laboured, grunting, or noisy breathing
• 🚨 Lips, tongue, or fingernails turning blue or pale
• 🚨 Unresponsive or unusually limp — floppy, difficult to rouse, won't make eye contact
• 🚨 Persistent crying that is not consolable and sounds different from normal
• 🚨 Bulging fontanelle — the soft spot on the head appears swollen or tight
• 🚨 Febrile seizure (fit associated with high fever) — call 999; lay them on their side, do not restrain, time it
• 🚨 Fever above 40°C at any age
• 🚨 Fever lasting more than 5 days at any age

When in doubt, always seek medical advice. You know your baby best — if something feels wrong, trust that instinct.

How to Take a Baby's Temperature Accurately

Digital Rectal Thermometer (Under 3 Months — Most Accurate)

• Apply a small amount of petroleum jelly to the tip
• Lay your baby on their back, holding both ankles to lift the bottom
• Insert the thermometer 1–2 cm (half to three-quarters of an inch) — no further
• Hold in place until it beeps — usually about 1 minute
• Normal rectal temperature: 36.6–38°C

Temporal (Forehead) Thermometer (3 Months+)

• Swipe across the forehead from the centre to the hairline, following the manufacturer's instructions
• Quick and convenient for home monitoring; accuracy is reasonable in older babies
• Less accurate if the baby is sweating or has been outdoors

Axillary (Armpit) Thermometer (All Ages)

• Hold the thermometer snugly under the armpit, with the arm against the body
• Hold for the required time (check your model — usually 1–2 minutes)
• Add 0.3–0.5°C to the reading for a more accurate core temperature estimate

Ear (Tympanic) Thermometer

• Avoid in babies under 6 months — the small ear canal makes readings inaccurate
• Suitable from 6 months with correct technique (gently pull the ear back and up to straighten the canal)

Do not rely on feeling a forehead with your hand — this is too inaccurate for clinical decision-making, though useful for noticing a change.

Managing Fever at Home (Babies Over 3 Months)

Fever-Reducing Medicines

Infant paracetamol (Calpol or equivalent):

• From 2 months of age (minimum 4kg; not for premature babies without medical advice)
• Dose is based on weight, not age — check the packaging for the correct amount
• Can be given every 4–6 hours, maximum 4 doses in 24 hours

Infant ibuprofen:

• From 3 months (minimum 5kg)
• Do not give to babies who are dehydrated, vomiting, or have kidney problems
• Do not give if your baby has chickenpox
• Can be given every 6–8 hours, maximum 3 doses in 24 hours

Do not give both medicines at the same time unless your doctor specifically advises it. Do not give aspirin to children under 16 — ever.

Comfort and Hydration

• Offer feeds frequently — breast milk or formula for babies under 6 months; water can be offered alongside milk from 6 months
• Signs of dehydration: fewer wet nappies than usual, a dry mouth, no tears when crying, sunken fontanelle, or listlessness
• Dress in a single layer of lightweight clothing — do not overbundle
• Keep the room at a comfortable temperature — not too warm
• Skin-to-skin can be calming during mild fevers in young babies

What Not to Do

• ❌ Cold baths or cold compresses — these cause shivering, which paradoxically raises core temperature
• ❌ Aspirin — never give aspirin to anyone under 16 (risk of Reye's syndrome)
• ❌ Fan blowing directly on a baby — causes shivering
• ❌ Undressing completely — causes heat loss through shivering, not fever reduction

Common Causes of Fever in Babies

A cause isn't always immediately obvious at home — your doctor will examine your baby to identify it.

Fever Myths Debunked

Myth: Fever damages the brain

Only temperatures above 42°C (extremely rare and usually associated with external heat sources like heatstroke, not illness) can cause brain damage. Standard illness fevers do not.

Myth: You must bring the fever down immediately

Fever is part of the immune response. There is no clinical benefit to treating a low-grade fever in a comfortable, well-hydrated baby over 6 months unless it is causing distress. Treat the child, not the number on the thermometer.

Myth: Teething causes high fever

Teething does not cause temperatures above 38°C. Any genuine fever during teething needs investigating separately.

Myth: A higher temperature means a more serious illness

Temperature does not reliably predict severity. A baby with meningitis may have a lower fever than a baby with a mild viral infection. How the baby looks and behaves matters more than the number.

Febrile Seizures

A febrile seizure is a fit triggered by rapid temperature change. They affect 2–4% of children under 5 and are frightening but usually harmless.

During a febrile seizure:

• Place the child on their side (recovery position) on a soft surface
• Time the seizure
• Do not put anything in their mouth
• Stay with them — call 999 if it lasts more than 5 minutes

After the seizure: Call your GP or go to A&E even if the child seems recovered. All first febrile seizures need medical evaluation.

Most febrile seizures last under 5 minutes, stop on their own, and cause no lasting harm. However, children who have had one febrile seizure are at slightly higher risk of another.

Keeping Records for Your Doctor

When you speak to your doctor, have ready:

• Your baby's temperature and when it started
• How long the fever has lasted and whether it has fluctuated
• Other symptoms: cough, rash, nappy output, feeding changes, behaviour changes
• Any medicines given, the dose, and the time given
• Recent vaccinations (date and which vaccines)
• Recent travel or contact with sick people

A quick note in your phone when you first notice the fever saves valuable time and helps your doctor make a faster assessment.