Dr. Greene’s Answer:
A wall of bone protects your baby’s brain; but at the “soft spot,” only soft, squishy tissue separates the brain from the traumas of the outside world. The soft spot seems so vulnerable. I’ve spoken with mothers who had never touched their babies’ soft spots — they were afraid they would put their fingers through it.
The medical word for soft spot is fontanel. Fontanels are examples of the amazing design of the human body. At birth, there are six fontanels, but only two are noticeable (the largest, up on top, is the anterior fontanel). The loose connections of the skull bones that intersect in the soft spots make labor and delivery possible. Without this flexible anatomy, either human babies would have to have smaller brains, or human mothers would have to have wider hips!
The value of the soft spot isn’t gone when you first hold your baby in your arms. Far from making the baby more vulnerable, the soft spot protects a baby from injury. Although the spot is soft, it actually consists of a surprisingly tough fibrous membrane. True, it can make some rare accidents more dangerous (direct penetrating trauma to that spot), but for the common falls experienced by all babies, the soft spot cushions and protects — making the skull function rather like a football helmet.
Every week, frantic parents rush into my office after their babies have fallen off a bed, table, or highchair. It happens so quickly, babies can fall even with careful and attentive parents — it’s even happened to me, but don’t tell :^). When babies fall, they usually land head first, since their centers of gravity are in their heads (adults’ centers of gravity are in our bottoms). The head hits the floor with a terrible, ripe-melon-like “thwunk.” Thanks to the cushioning of the soft spot, most of these head injuries are minor.
At birth, babies’ soft spots come in a very wide range of sizes. If the anterior fontanel is small, it will usually enlarge over the first several months. Conversely, large ones tend to get smaller. By the time a baby is 2 months old, the anterior fontanel is usually about 1 x 1 1/2 inches. The anterior fontanel is usually the last fontanel to disappear. For most kids, the anterior fontanel closes not long after they get steady on their feet (at 9 to 18 months), but the timing varies widely. It stays open just long enough to protect them as they stumble their way toward walking on their own. How quickly it all goes!