Why do babies have a soft spot on their head?
The soft spots are fontanelles — gaps where the skull bones have not yet fused, covered by tough membrane. They exist for two reasons, both essential.
Birth. A baby's head is the widest part to pass through the birth canal. Unfused skull plates can overlap and shift during delivery, temporarily narrowing the head. This is why many newborns have a slightly cone-shaped or moulded head for the first days — it resolves on its own.
Brain growth. The brain roughly doubles in volume in the first year. A fused skull could not accommodate that. Open sutures and fontanelles allow the skull to expand with the brain beneath it.
There are two main fontanelles:
The posterior fontanelle, at the back, is small and typically closes by around two months.
The anterior fontanelle, on top and diamond-shaped, is the one people notice. It usually closes between 9 and 18 months, though the range is wide.
What is normal: a flat or very slightly curved surface; visible pulsation matching the heartbeat, which is entirely normal and simply blood flow; and slight bulging when a baby cries, strains or lies down, settling when calm and upright.
Touching it is fine. The membrane is genuinely tough, and normal handling, washing and brushing hair will not hurt the baby. Many parents avoid the area unnecessarily, and cradle cap is often worse there as a result.
When to seek medical advice:
A sunken fontanelle in a settled baby can indicate dehydration, particularly alongside fewer wet nappies, dry mouth or lethargy. This warrants prompt assessment.
A bulging, tense fontanelle in a calm, upright baby — especially with fever, vomiting, unusual drowsiness, a high-pitched cry or a rash — needs urgent medical attention, as it can indicate raised pressure inside the skull.
Very early or very late closure is worth mentioning at a routine check.