A Baby's Soft Spot

When to get help

Call emergency services now — 999 in the UK, 112 or 999 in Ireland and across the EU, 911 in the US and Canada, 000 in Australia, 111 in New Zealand — if the soft spot on the top of your baby's head is bulging, tense or firm while your baby is calm and held upright. NICE guideline NG143 lists a bulging fontanelle as a red feature in a child with fever, in the same group as a non-blanching rash, neck stiffness and status epilepticus. The Meningitis Research Foundation lists it among the signs of meningitis in babies.

Call emergency services too if a bulging soft spot follows a fall or a blow to the head. NICE guideline NG232 tells clinicians to arrange a CT head scan within one hour of identifying a tense fontanelle after a head injury in a person under 16.

Seek urgent same-day advice — NHS 111 in the UK, your GP or out-of-hours service in Ireland, your paediatrician in the US or Canada, healthdirect on 1800 022 222 in Australia, Healthline on 0800 611 116 in New Zealand — if the soft spot looks sunken and your baby has had fewer wet nappies than usual, has been vomiting or has diarrhoea. A sunken fontanelle is one of the signs of dehydration listed by both the NHS and the American Academy of Pediatrics, and dehydration in a small baby moves quickly.

What the soft spot actually is

A baby's skull is not one piece of bone. It is several plates with gaps between them, which is what allows the head to compress slightly during birth and then to grow fast in the first year. The gaps are called fontanelles, and they are covered by tough membrane, not by nothing. You cannot damage the brain by washing that part of the head or brushing over it, and cradle cap on the fontanelle is treated like cradle cap anywhere else.

There are two you can usually feel. The one everybody knows is the anterior fontanelle, the diamond-shaped soft area towards the front of the top of the head, which typically closes somewhere between about one year and two. The smaller posterior fontanelle, towards the back, is often already too small to find by two or three months.

What normal feels like

With your baby calm and held upright, the anterior fontanelle should feel flat or very slightly dipped, and soft rather than tight. You will often see or feel it pulsing gently in time with the heartbeat. That pulsing is normal and is not a sign of anything wrong.

Position and effort change it. It commonly bulges when a baby cries hard, strains, coughs or is lying flat, and it settles again once they are calm and upright. That is why the way to check is always the same: pick your baby up, wait for the crying to stop, then look and feel. A bulge that disappears when your baby calms down is normal. A bulge that is still there on a settled, upright baby is the one that matters.

Size varies enormously between babies and tells you very little on its own. A large fontanelle in an otherwise thriving baby is usually just a large fontanelle.

Bulging: what it can mean

A persistently tense or bulging fontanelle means raised pressure inside the head. The causes that matter most in a baby are infection of the linings of the brain, bleeding after a head injury, and a build-up of fluid. None of those are diagnosable at home, and none of them wait.

Look at what else is happening in the same hour, because a bulging fontanelle almost never travels alone. Fever, a high-pitched or moaning cry, unusual drowsiness or floppiness, vomiting, a stiff neck, a dislike of bright light, a blotchy rash that does not fade under a glass, or a seizure alongside a bulging soft spot all point the same way: emergency services, now, not a call-back in the morning.

Sunken: what it can mean

A definitely sunken fontanelle, one that looks like a shallow dip you can see across the room rather than feel with a fingertip, is a late sign of dehydration in a baby. It arrives after the earlier signs, which is exactly why it is not the sign to wait for.

The earlier ones are easier to catch. Fewer wet nappies than usual, dark and strong-smelling urine, a dry mouth and tongue, no tears when crying, unusual sleepiness or irritability, and cold or blotchy hands and feet. Those are what the NHS and the AAP list, and in a baby who is vomiting or has diarrhoea they can appear within hours rather than days.

If your baby is dehydrated the answer is not water. Under six months, keep offering breast milk or formula more often and in smaller amounts, and ring for advice about whether an oral rehydration solution is needed. Older babies who have started solids still get their fluid mainly from milk. Never dilute formula to make a baby drink more of it.

Checking it properly

Do this in good light with your baby upright and not crying, ideally after a feed rather than during one. Place the flat pads of two fingers gently over the soft area — you are feeling for tension, not pressing in. Compare with what you remember from a settled day. Take a photo from the side in the same light if you want something to compare against later; a description of change over hours is far more useful to a clinician than one snapshot.

Do not press hard, and do not let a well-meaning relative demonstrate on your baby's head. There is no home test that needs force.

When to raise it without an emergency

Some fontanelle questions belong at a routine review rather than in an ambulance. A soft spot that seems to be closing very early, one that is still clearly open well past the second birthday, a head that is growing much faster or much more slowly than the centile chart suggests, or a persistent ridge along a skull suture are all worth raising with a health visitor, public health nurse or paediatrician so the head circumference can be measured and plotted properly.

Those are appointments. A tense, bulging fontanelle on a calm, upright baby is not.