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A bulging fontanelle in a baby is a red flag on every list published for young babies. NICE names it in both of the guidelines that matter here: it is one of the red flags for serious illness in young babies in the postnatal care guideline NG194, and it sits in the high-risk red column of the traffic light system in the fever guideline NG143. NICE also tells clinicians to consider bacterial meningitis in a child with fever and a bulging fontanelle.

If your baby's soft spot is domed or tense when they are calm and upright — not while they are crying or straining — call your local emergency number: 999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand. The NHS lists a bulging fontanelle among the symptoms of meningitis in babies, alongside a high temperature, being unusually sleepy or difficult to wake, a rash that does not fade under a glass, and a stiff neck.

A deeply sunken fontanelle is the other emergency. The HSE lists a sunken soft spot among the signs of dehydration in babies, together with fewer wet nappies, no tears when crying, a dry mouth, drowsiness and cold, blotchy hands and feet. Dehydration in a newborn moves fast and should be assessed the same day.

What the fontanelles are

The NHS describes them exactly: "On the top of your baby's head, near the front, is a diamond-shaped patch where the skull bones have not fused together yet. There is another, smaller, soft spot towards the back of their head. These are called the fontanelles."

They exist for two reasons. They let the skull bones overlap and change shape as your baby passes through the birth canal, and they let the skull keep growing while the brain does most of its early growing.

The AAP says the same thing and adds the reassurance parents most need: "All babies have two soft spots, or fontanelles, on the head... Parents needn't be afraid to touch these areas gently, as there is a thick, durable membrane that protects the brain." The NHS's wording is near-identical: "Do not worry about touching the fontanelles as they are covered by a tough protective membrane."

When it closes

The NHS gives one figure: "It will probably be a year or more before the bones close over." The smaller fontanelle at the back closes considerably earlier than the one at the front. Beyond that, published parent-facing guidance is deliberately vague, and there is no single age at which a fontanelle is supposed to be shut. Health services do not publish a home-checkable timetable, so this page will not invent one.

What is checked, and by whom, is worth knowing. NICE NG194 specifies that the complete newborn examination within 72 hours of birth and again at six to eight weeks includes the head and fontanelles, and that head circumference is measured in the first week and at around eight weeks and plotted on a growth chart. That plotted line, not the feel of the soft spot, is how professionals track skull growth.

What is normal

It pulses. You can often see a rhythmic movement in time with your baby's heartbeat. That is blood flow through vessels under a thin membrane, and it is expected.
It moves when they cry, strain, cough or vomit. Pressure inside the head rises briefly with all of those, so the soft spot rises briefly too. It should settle within moments of your baby calming, and it should be assessed when your baby is calm and held upright.
It feels flat or very slightly dipped when your baby is calm and upright, and slightly fuller when they are lying down.
It is safe to wash and brush over. Both the NHS and the AAP say so. Cradle cap treatment, hair washing and gentle brushing over the fontanelle are all fine.
It gets relatively smaller over months as the surrounding bone grows.

What a newborn head looks like early on

Two other findings are often confused with the fontanelle. The AAP describes caput — scalp swelling in the area pushed out first during birth, which can hold a fingerprint when pressed and "should disappear in a few days". And cephalohaematoma — firmer swelling on one or both sides that springs back when pressed, caused by bleeding along the outer side of the skull bones, not inside the brain, which the AAP says "usually takes six to ten weeks to disappear". Neither is the soft spot, and neither is dangerous in itself.

How to check it properly

The soft spot is only interpretable under the right conditions, and getting these wrong is the main reason parents frighten themselves.

Your baby should be calm — not crying, straining or feeding.
Your baby should be upright, held against your shoulder or sitting supported. A soft spot always looks fuller in a baby lying flat.
Use flat fingers, gently. You are feeling for a dome or a dip, not pressing in.
Compare with what it usually feels like. You are the person who knows the baseline.

When to call

Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand) if your baby:

Has a bulging or tense fontanelle when calm and upright.
Has a temperature of 38C (100.4F) or above, or below 36C (96.8F).
Has a rash that does not fade when you press a clear glass against it.
Is unresponsive or unrousable, or has a weak, abnormally high-pitched or continuous cry.
Has a stiff neck, a seizure, or dislikes being handled and arches their back.
Looks pale, ashen, mottled or blue, is grunting, or is breathing over 60 breaths a minute.

Those are NICE's NG194 red flags for young babies, and the NHS's meningitis symptom list for babies overlaps them almost exactly.

Get same-day advice from your midwife, health visitor, public health nurse, GP or an out-of-hours service if: the fontanelle looks sunken, your baby is having fewer wet nappies than usual, has a dry mouth or no tears when crying, is unusually drowsy, or is feeding poorly. NICE lists reduced urine output and poor feeding as intermediate-risk amber signs; the HSE lists a sunken soft spot as a sign of dehydration.

What to let go of

You cannot damage your baby's brain by washing their hair, putting on a hat, or resting your hand on their head. The membrane is described as tough and durable by both the NHS and the AAP. A soft spot that pulses is not a problem; a soft spot that changes shape when your baby cries is not a problem either. The two states that matter are domed when calm, and clearly hollowed — and both of those have a phone number attached rather than a home remedy.

Newborn Soft Spot