Your baby's fontanelle: normal changes and warning signs
That soft, slightly pulsing patch on your newborn's head can feel alarming the first time you notice it. You might worry about touching it, or wonder what the gentle rhythmic movement means. The good news is that fontanelles are an entirely normal part of how your baby's skull develops, and most of the time what you are seeing is perfectly fine. This guide explains what to expect, what is normal, and the handful of signs that genuinely need attention.
What fontanelles are and why they exist
Your baby's skull is not a single solid bone at birth. It is made up of several separate bony plates joined by flexible fibrous tissue called sutures. Where multiple sutures meet, you get a fontanelle: a gap in the bone covered only by a tough, protective membrane.
This design is intentional. During birth, the bony plates can gently overlap and shift, allowing your baby's head to fit through the birth canal. In the months that follow, the gaps leave room for the rapid brain growth that happens in the first two years of life. Without this flexibility, there would simply not be enough space.
The two fontanelles and where to find them
Most babies have two fontanelles that you might notice:
The anterior fontanelle is the one most parents notice. It sits at the top of the head toward the front, roughly where a headband would sit, and has a diamond or rhombus shape. It is typically around 2 to 3 centimetres across at birth, though there is quite a bit of natural variation. The anterior fontanelle closes gradually as the skull bones grow together, usually between 12 and 18 months (the NHS notes that anywhere from 9 to 24 months is within the normal range).
The posterior fontanelle is much smaller, triangular, and sits at the back of the head where the skull meets the neck. Many parents never notice it at all. It closes much earlier, typically by 6 to 8 weeks, and almost always by 3 months.
What a normal fontanelle looks and feels like
When you look at or gently feel the fontanelle, here is what is normal:
- Slight inward curve. When your baby is calm and sitting or held upright, the fontanelle may sit very slightly below the level of the surrounding skull. This is normal.
- A gentle pulse. You may see or feel a slow, rhythmic pulsing that matches your baby's heartbeat. This is the normal pressure of blood circulating close to the surface of the brain coming through. It can look quite visible in younger babies with fine hair and is completely harmless.
- Temporary bulging when crying. When your baby cries, strains, holds their breath, or is briefly tipped upside down, the fontanelle can bulge outward. This is a normal response to the temporary increase in pressure inside the head. It resolves as soon as your baby settles down.
Signs that need prompt attention: sunken fontanelle
A fontanelle that looks noticeably hollow or pulled in when your baby is calm and upright can be a sign of dehydration. When the body does not have enough fluid, the tissue around the brain reduces in volume and the fontanelle sinks inward.
Watch for a sunken fontanelle alongside any of these signs of dehydration: fewer wet nappies than usual (less than six in 24 hours for a young baby), a dry mouth, sunken eyes, or a baby who seems unusually drowsy or difficult to rouse. If you notice these signs together, contact your GP or NHS 111 on the same day. Dehydration in a young baby can progress quickly and needs assessment.
Signs that need urgent attention: persistently bulging fontanelle
A fontanelle that bulges outward when your baby is calm, upright, and not crying is different from the normal temporary bulging described above. A persistent bulge in a resting baby can indicate that pressure inside the skull is raised, which may be caused by a serious infection such as meningitis or encephalitis, or by a build-up of fluid around the brain.
Call 999 or go to your nearest emergency department immediately if your baby has a bulging fontanelle at rest, especially if they also have any of the following: fever, a high-pitched or unusual cry, sensitivity to light, drowsiness that is hard to rouse them from, a rash that does not fade under a glass, vomiting, or seizures. Do not wait to see if it improves. Bacterial meningitis in particular is a medical emergency where time matters.
Early fontanelle closure: when to mention it to your doctor
Rarely, the skull bones can begin to fuse too early, a condition called craniosynostosis. When this happens, it restricts the space for brain growth and can change the shape of the skull. It affects around 1 in 2,000 to 2,500 babies (NHS data) and is not caused by anything parents did or did not do.
Signs that might prompt your GP or health visitor to refer for assessment include a fontanelle that appears to close very early (before 6 months), an asymmetrical or unusually shaped skull that is not improving, or a ridge you can feel along a suture line. Most head shape variations are harmless positional flattening rather than craniosynostosis, but your GP can examine the skull and refer if needed.
Can you touch the fontanelle?
Yes, and you do not need to be especially careful. The fontanelle is covered by a tough, fibrous membrane that is durable enough to protect the brain during normal daily life. Washing your baby's hair, normal cuddles, and gentle touch will not cause any harm. Many parents feel anxious about the area, but routine contact is perfectly safe.
Tracking your baby's development
Health visitors routinely check the fontanelle at your baby's scheduled checks. If you ever feel uncertain about how the fontanelle looks or feels between appointments, it is always fine to contact your health visitor or GP. Checking these things is exactly what they are there for.
Frequently asked questions
Is it normal for the fontanelle to pulse?
Yes, completely normal. You may see a gentle pulsing in time with your baby's heartbeat, particularly over the larger front soft spot. This reflects the normal pressure of blood circulating through the brain and is not a cause for concern.
What does a sunken fontanelle mean?
A fontanelle that looks noticeably hollow or pulled inward when your baby is calm and upright can be a sign of dehydration. If your baby has also been feeding poorly, producing fewer wet nappies, or has been unwell with vomiting or diarrhoea, contact your GP or NHS 111 the same day.
Should the fontanelle bulge when my baby cries?
Yes. When your baby cries, holds their breath, or is upside down, the fontanelle will bulge temporarily. This is completely normal and disappears as soon as your baby settles. The concern is a fontanelle that bulges persistently when your baby is calm, upright, and not crying.
When does the fontanelle close?
The posterior fontanelle (at the back of the head) usually closes by 2 to 3 months. The larger anterior fontanelle (at the front) typically closes between 12 and 18 months, though anywhere between 9 months and 24 months is within the normal range according to the NHS.
Can I touch my baby's fontanelle?
Yes. The fontanelle feels soft but it is protected by a tough, durable membrane. Normal handling, washing your baby's hair, and gentle touch will not cause any harm. You do not need to avoid the area.
What does a persistently bulging fontanelle mean?
A fontanelle that bulges when your baby is calm, upright, and relaxed (not crying) can indicate raised pressure inside the skull. This needs urgent medical assessment. Call 999 or go to your nearest emergency department, particularly if your baby also has a fever, is unwell, seems drowsy, or has a high-pitched cry.
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