Key point: a fontanelle is a normal part of an infant’s skull, not an “open” area that leaves the brain unprotected. Its appearance can vary with position, crying and the baby’s overall condition. In France, Assurance Maladie states that the small posterior fontanelle usually closes between 2 and 4 months and the large anterior fontanelle between 9 and 18 months. These are reference ranges, not individual deadlines: clinicians interpret them alongside skull shape, the head-circumference curve, growth and development.
This guide helps parents understand what they may notice at home without turning the fontanelle into a home diagnostic test. A fontanelle that looks sunken or bulging cannot be interpreted reliably on its own.
What is a fontanelle?
A newborn’s skull is made up of several bones separated by sutures. At some of the points where these bones meet are membranous spaces called fontanelles. The best known is the anterior fontanelle on the top of the head. A much smaller posterior fontanelle is located toward the back.
These areas are made of strong tissue and covered by the scalp. A fontanelle is therefore not a “hole” providing direct access to the brain. Healthcare professionals routinely feel it during an infant examination.
Why do fontanelles exist?
Sutures and fontanelles allow the skull to adapt around birth and, above all, to accommodate the brain’s rapid growth early in life. Their gradual closure is part of normal development.
Closure of a fontanelle does not mean that the skull stops growing. Assurance Maladie notes that the skull continues to grow after the fontanelles close, simply at a much slower rate.
Can you touch a baby’s fontanelle?
Yes, gently. Washing and drying the hair, routine scalp care and stroking the head are all compatible with the presence of a fontanelle. The head should of course be protected from injury like any infant’s head, but there is no need to avoid all contact with this area.
Why can it appear to pulse?
A slight pulsation can sometimes be visible because the tissues in this area transmit movements related to blood circulation. In a baby who is otherwise well, an isolated visible pulse is not in itself an emergency sign.
Why does its appearance change with position or crying?
A baby’s position and straining can temporarily change the appearance of the fontanelle. It may look fuller when a child cries, coughs or strains and different when lying down. This is one reason why a fontanelle thought to be “bulging” is best assessed when the infant is calm and within the full clinical context.
A photograph taken at one moment cannot accurately assess its tension. Touch, the baby’s behaviour and other clinical signs matter far more.
When do fontanelles close?
For French reference ranges, Assurance Maladie states that the small posterior fontanelle closes between 2 and 4 months and the large anterior fontanelle between 9 and 18 months. Another Ameli page about cradle cap gives a broader range of 8 to 24 months for the large fontanelle. This difference itself illustrates normal variability and why a single age should not be used as a diagnostic cut-off at home.
International sources also give somewhat different ranges. Rather than searching for a single “perfect” date, paediatric follow-up considers the overall pattern: fontanelle size, skull shape, sutures, head circumference and development.
Why is head circumference measured?
In France, doctors regularly measure an infant’s head circumference and plot the values on the growth chart in the child health record. A series of measurements can reveal an acceleration or, conversely, a slowdown in head growth.
This trajectory is more informative than trying to measure the fontanelle yourself. Two babies of the same age can have different-sized fontanelles while both are developing normally.
Should you measure the fontanelle at home?
No, this is generally not useful. Repeated home measurements can create unnecessary anxiety and may be inaccurate. A clinician assesses the size and tension of the fontanelle together with the rest of the examination.
A fontanelle that looks very sunken
A clearly sunken fontanelle can be one of the findings seen with dehydration, but it can never establish that diagnosis on its own. The whole baby must be considered: how much they are drinking, urine output and wet nappies, mouth, tears, behaviour, vomiting or diarrhoea, and overall condition.
If an infant is drinking much less than usual, is vomiting or has diarrhoea and is wetting far fewer nappies, professional advice is appropriate. In a very young infant, any deterioration in general condition deserves particular caution.
A fontanelle that looks very full or bulging
A fontanelle can temporarily look fuller during crying or straining. However, a fontanelle that remains clearly tense or bulging when the baby is calm, particularly if accompanied by fever, unusual drowsiness, marked irritability, vomiting, a seizure or another change in general condition, requires prompt medical assessment.
Parents cannot determine the cause simply by looking at the fontanelle. The same apparent appearance can have different meanings depending on the context.
Bulging fontanelle and meningitis: never rely on one sign
A bulging fontanelle can be among the signs seen in some serious infections, but not every affected infant has this sign, and a fontanelle that appears full does not automatically mean meningitis. In babies, the combination of symptoms and the overall condition should guide the response.
An infant who is difficult to wake, very listless, having a seizure, struggling to breathe, showing unusual skin colour, developing a rash that does not fade under pressure, or deteriorating rapidly needs urgent assessment regardless of the fontanelle’s appearance.
What other signs matter?
In an infant, assessment always considers the whole child: temperature, breathing, colour, responsiveness, feeding, urine output, vomiting, behaviour and any neurological signs. A change in the fontanelle is therefore never interpreted in isolation.
For fever, see our guide Baby fever: temperature and when to seek medical advice for the main safety points.
Fontanelle and head shape
An asymmetrical head shape may be positional, as in some cases of plagiocephaly, but certain abnormalities of the skull sutures require specialist assessment. Premature fusion of one or more sutures is called craniosynostosis.
Craniosynostosis is not diagnosed simply because a parent can no longer feel the fontanelle. Head shape and the evolution of head circumference are important. Our guide to flat head and plagiocephaly explains positioning measures and when professional advice is useful.
Early closure: should you worry?
Not automatically. A fontanelle can become small or difficult to feel while skull growth remains normal. Clinicians mainly assess head shape, the head-circumference trajectory, the sutures and the child’s development.
Conversely, an unusual head shape or concerning growth trajectory deserves assessment even if a parent believes the fontanelle is still open. What can or cannot be felt at home is not an adequate screening test.
Late closure
A fontanelle that remains open beyond usual reference ranges can sometimes be an individual variation. Some medical conditions can also be associated with later closure. This is why the finding is best interpreted as part of the child’s follow-up rather than diagnosed from internet comparisons.
Vitamin D and the fontanelle
Vitamin D contributes to bone health, but the appearance or size of the fontanelle cannot determine the dose an infant needs. Supplementation should follow recommendations and the prescription appropriate for the child. Never change a dose in an attempt to make a fontanelle close faster.
Sleep and the fontanelle
The fontanelle does not require a special sleeping position. Safe-sleep recommendations remain the same: place the baby on their back, on a firm, clear sleep surface, in an appropriate sleep environment.
For early sleep patterns, see Newborn sleep: how many hours and when to be concerned?.
Hat, carrier or protective gear: does the fontanelle need special protection?
No, not in everyday life. There is no need to add padding over the fontanelle. Standard safety rules are enough: handle the infant carefully, use age-appropriate equipment correctly and prevent head injuries.
After a bump to the head: does the fontanelle change what you should do?
After a head injury, severity is not judged by looking only at the fontanelle. The baby’s age, how the injury happened, any fall height, behaviour, vomiting, loss of consciousness, unusual drowsiness and neurological abnormalities matter much more. For an infant, seek medical advice if you are unsure after a significant head impact.
What to avoid
- Measuring the fontanelle every week at home.
- Diagnosing dehydration from its appearance alone.
- Assuming a skull abnormality simply because it seems small or can no longer be felt.
- Changing vitamin D supplementation without professional advice.
- Obsessively comparing the fontanelle with online photographs.
- Delaying medical advice when the baby’s overall condition is concerning.
When should you seek advice?
Speak to the healthcare professional following your child if the fontanelle changes clearly and persistently, if the head shape looks unusual, if the growth curve concerns you, or if closure seems very different from usual reference ranges.
Prompt assessment is particularly important when a fontanelle change occurs with a baby who is very sleepy or difficult to wake, feeding very poorly, has a fever, repeated vomiting, a seizure, breathing difficulty or a marked deterioration in overall condition.
FAQ
Is the fontanelle a hole in the skull?
No. It is a membranous area between several skull bones, covered by protective tissues and skin.
Can you touch it?
Yes. Routine care and gentle touch are safe.
Is it normal to see it pulse?
A slight pulsation can be visible in a healthy baby.
Why does it change when a baby cries?
Straining and position can temporarily alter its appearance.
When does the large fontanelle close?
Assurance Maladie gives a reference range of 9 to 18 months in its infant follow-up information. Another Ameli page gives 8 to 24 months, highlighting individual variability and the need to interpret closure alongside the rest of the examination.
What about the fontanelle at the back?
The posterior fontanelle usually closes much earlier; Ameli gives 2 to 4 months.
Does a sunken fontanelle always mean dehydration?
No. It can contribute to the assessment, but hydration is judged using several other signs.
Is a fuller fontanelle during crying always abnormal?
No. Its appearance must be interpreted in context and, in particular, reassessed when the child is calm.
If I can no longer feel it, has the skull stopped growing?
No. Skull growth continues after the fontanelles close.
Can a photograph tell whether it is normal?
Not reliably. Touch, position and a clinical examination provide information that a photograph cannot.
Should I press on it to check whether it is sunken or bulging?
No. There is no need to perform pressure tests yourself. If its appearance concerns you, have it examined.
Read more on Confort Enceinte
- Baby fever: temperature and when to seek medical advice
- Flat head and plagiocephaly
- Newborn sleep
- Infant bowel movements: stools and when to seek advice
Sources
- Assurance Maladie — Medical follow-up up to 2 months.
- Assurance Maladie — Infant follow-up from 3 to 18 months.
- Assurance Maladie — Cradle cap and fontanelle information.
- MedlinePlus — Fontanelles.
- MedlinePlus — Bulging fontanelles.
- MedlinePlus — Sunken fontanelles.
- NHS — Dehydration.
- NHS — Meningitis symptoms.
- American Academy of Pediatrics / HealthyChildren — Craniosynostosis.
Enhanced evidence review: 5 October 2026. General information only; an infant’s overall condition always matters more than an isolated interpretation of the fontanelle.
Leave a comment: