Understanding Your Baby's Soft Spot (Fontanelle): What's Normal

The first time you feel it — that slight give in the top of your baby's head — it can feel alarming. But the fontanelle (or fontanel) is one of the most elegant engineering solutions in the human body: the skull doesn't fully fuse at birth so the head can compress through the birth canal and then expand as the brain grows rapidly in the first years of life.

What Is the Fontanelle?

The fontanelle is the soft area on a baby's skull where the cranial bones haven't yet fused. At birth, a baby has multiple fontanelles, but there are two that parents typically encounter:

Anterior fontanelle (front soft spot): Located at the top of the head, where the frontal and parietal bones meet. It's diamond-shaped, typically 1–3 cm in diameter at birth, and the one parents notice most. This closes between 9–18 months.

Posterior fontanelle (back soft spot): Located at the back of the head, where the parietal and occipital bones meet. Smaller — often fingertip-sized — and closes by 6–8 weeks in most babies.

What's Normal to See and Feel

In a healthy baby, the anterior fontanelle should feel:

• Soft and flat when the baby is calm in a sitting or semi-upright position
• Pulsing slightly — you may feel the baby's heartbeat through it; this is normal
• Slightly fuller when the baby cries or strains; this is due to increased blood flow and pressure, not a sign of a problem

Normal variations:

• The fontanelle can look like it's moving with the heartbeat — this is expected and harmless
• It may look slightly sunken when a baby is in an upright position — gravity affects it
• It can appear fuller in a newborn and gradually become less prominent

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When Does the Fontanelle Close?

Source: AAP developmental standards; Nelson's Textbook of Pediatrics

Early closure (craniosynostosis): When the sutures fuse too early, the skull can't expand normally with the growing brain. Signs include an abnormal head shape, a raised ridge along the suture lines, or a head circumference that is not growing. This is rare (about 1 in 2,000 births) but requires evaluation.

Late closure: A fontanelle still open at 24 months warrants investigation. Possible causes include hypothyroidism, rickets, Down syndrome, or bone development disorders.

Warning Signs: When to Call Your Doctor

Most fontanelle concerns don't require emergency care, but some do.

Call your pediatrician within 24 hours if:

• Your baby's fontanelle looks consistently more sunken than usual alongside dry diapers or lethargy
• You notice an unusual bulge, ridge, or asymmetry developing along the scalp
• The anterior fontanelle closed before 8 months of age
• Head circumference growth appears to have slowed significantly

Go to the emergency room immediately if:

• The fontanelle is bulging and tense when your baby is NOT crying or straining
• Bulging fontanelle + fever (possible meningitis)
• Bulging fontanelle + vomiting + irritability + neck stiffness
• Sunken fontanelle + baby is very lethargic, eyes are sunken, no wet diapers in 8+ hours (severe dehydration)

Measuring Head Circumference at Well-Child Visits

Your pediatrician measures head circumference at every well-child visit in the first two years. This measurement tracks brain growth over time and is often more clinically meaningful than a single fontanelle observation.

Growth velocity — how fast the head is growing — matters more than any single measurement. A head circumference that is consistently on the 10th percentile and tracking that curve is perfectly healthy. It's when the curve changes dramatically (rapid crossing of percentile lines upward or downward) that investigation is warranted.

The Takeaway

The fontanelle exists for good reason and is robustly protected by tough fibrous tissue. You can wash your baby’s hair, wear a carrier, and cuddle gently without any concern about the soft spot. The key signs to know: a flat, slightly pulsing fontanelle in a calm, alert baby is normal. Bulging when calm is an emergency. Deeply sunken with signs of dehydration is urgent. Everything else can usually wait for a scheduled call to your pediatrician.