A fontanel is a soft spot on a baby’s skull where the bones haven’t yet fused together. These gaps, made of tough connective tissue, sit between the bony plates of an infant’s head and serve two critical purposes: they let the skull compress during birth, and they give the brain room to grow rapidly in the first year of life. Every baby is born with multiple fontanels, and they’re a completely normal part of infant anatomy.
Where Fontanels Are Located
Newborns have six fontanels, though only two are easy to feel. The anterior fontanel sits on top of the head, slightly toward the front. It’s diamond-shaped and averages about 2.1 centimeters across. This is the one most parents notice and the one pediatricians check at every wellness visit. The posterior fontanel is at the back of the skull, triangle-shaped, and much smaller, roughly the size of a fingertip.
The remaining four fontanels are located on the sides of the skull, two on each side. These are called the sphenoidal fontanels (near the temples) and the mastoid fontanels (behind the ears). They’re smaller and harder to detect, but a doctor can feel them during a careful exam.
Why Babies Need Soft Spots
During vaginal delivery, the skull bones need to shift and overlap slightly so the baby’s head can pass through the birth canal. The fontanels and the seams (sutures) connecting the skull bones make this possible. Without these flexible gaps, the rigid skull would be too large to navigate the narrow passage safely.
After birth, fontanels take on a second role. A newborn’s brain roughly triples in size during the first two years. The soft spots and open sutures give the skull the flexibility to expand along with that rapid brain growth. Once the brain reaches a more stable size, the bones gradually knit together and the fontanels disappear.
When Fontanels Close
The posterior fontanel, the small one at the back, typically closes by 1 to 2 months of age. The anterior fontanel stays open much longer, usually closing sometime between 7 and 19 months. The Mayo Clinic notes a typical range of 12 to 18 months. There’s natural variation from baby to baby, so closing at 9 months or 18 months can both be perfectly normal.
What a Normal Fontanel Looks and Feels Like
A healthy fontanel feels soft and roughly flat, sitting level with the surrounding skull. You may notice it pulsing gently in rhythm with your baby’s heartbeat. This is normal arterial pulsation, caused by blood flow near the surface. It’s especially visible in infants with strong pulses and is not a sign of a problem.
The fontanel can temporarily bulge when a baby cries, strains, or lies flat. This is also normal. If you’re unsure whether a fontanel is truly bulging or just reacting to crying, holding the baby upright in a sitting position gives a more accurate read, since gravity pulls fluid downward and lets the fontanel settle to its resting state.
Despite what many parents worry about, fontanels are safe to touch. You can gently wash over them, brush hair across them, and lightly feel them without harming your baby. The connective tissue covering the gap is tough and protective.
Sunken Fontanel: A Sign of Dehydration
A fontanel that dips inward, creating a visible dent like the dimple on a golf tee, often signals dehydration. The soft tissue over the gap loses some of its fullness when a baby’s fluid levels drop. Look for other clues alongside a sunken soft spot:
- Fewer wet diapers than usual
- Dry mouth or lips
- Few or no tears when crying
- Unusual sleepiness or fussiness
If you notice a sunken fontanel along with any of these signs, your baby likely needs fluids and medical attention promptly.
Bulging Fontanel: When Pressure Builds
A fontanel that stays raised and feels tense when the baby is calm and upright can indicate increased pressure inside the skull. Several serious conditions cause this kind of pressure, including meningitis (infection of the membranes around the brain), hydrocephalus (excess fluid buildup in the brain), encephalitis (brain inflammation), and bleeding inside the skull from trauma.
Other signs of elevated pressure in infants include persistent vomiting, excessive drowsiness, and irritability that doesn’t respond to normal soothing. A bulging fontanel that doesn’t go away when the baby is upright and quiet warrants immediate medical evaluation.
Early Closure: Craniosynostosis
When the skull’s sutures fuse too early, a condition called craniosynostosis, the fontanels may close prematurely. This restricts normal skull expansion. The brain keeps growing, but the skull can’t accommodate it evenly, leading to an abnormal head shape.
Which suture closes early determines the shape the head takes. Early closure along the top of the skull produces a long, narrow head. Early closure at the front creates a flattened forehead on one side, sometimes with a raised eye socket. When the suture running down the forehead closes too soon, the head narrows in front and widens in back. Each pattern has a distinct appearance that doctors are trained to recognize.
In most cases, the brain still grows to its normal size, just inside an unusually shaped skull. But when multiple sutures close early, the skull may not have enough room for the brain at all. Without treatment, this buildup of pressure can lead to vision loss, seizures, or brain damage.
The first sign is usually an abnormal head shape. Doctors also check for hard ridges along the sutures (where bone has fused prematurely) and the absence of a soft spot. If craniosynostosis is suspected, a CT scan confirms the diagnosis by showing exactly which sutures have closed. Most cases are treated with surgery to reopen the fused sutures and allow the skull to grow normally.
What Doctors Check at Wellness Visits
At routine checkups, your pediatrician will feel the anterior fontanel and sometimes the posterior one. They’re checking three things: the size of the fontanel relative to the baby’s age, whether it feels flat or abnormally tense, and whether the surrounding sutures are still open. They’ll also track head circumference over time, since a head that stops growing or grows too quickly can signal problems with fontanel and suture development.
A fontanel that’s slightly larger or smaller than average at a single visit is rarely a concern on its own. The trend over multiple visits matters more. A fontanel that’s growing larger instead of gradually shrinking, or one that disappears much earlier than expected, prompts closer evaluation.