A fontanel (also spelled fontanelle) is a soft spot on a baby's skull where the bones haven't yet grown together. If you've ever gently touched the top of a baby's head, you might have felt a place where the skull seems slightly squishy or where you can see a pulse. That's a fontanel.

Babies are born with fontanels because their skulls need to be flexible during birth, allowing the head to squeeze through the birth canal. After birth, these soft spots serve another important purpose: they give the baby's brain room to grow rapidly during the first year of life. The largest fontanel, on the top of the head, usually closes between 12 and 18 months of age as the skull bones gradually grow together and fuse.

Parents and doctors monitor fontanels carefully because they can reveal important information about a baby's health. A fontanel that bulges outward might signal increased pressure in the skull, while one that sinks inward could be a sign of dehydration.