Should I be concerned about the soft spot on my baby's head?

Q: The soft spot on my 4-month-old son's head seems to be pretty big—it's 2 3/4 inches by 2 1/2 inches—but my doctor says not to be concerned. What do you think?

A: Yes, it's bigger than average, and no, you don't need to worry about it. A very large fontanel, or "soft spot," can be a sign of extraordinarily rare diseases and syndromes like dwarfism or hydrocephalus, but believe me, your doctor would know if either of these conditions was present.

A baby's soft spot usually measures about 1 1/2 inches by 1 1/2 inches at 4 months of age; it gradually grows smaller until it completely closes, usually sometime between 1 and 2 years of age. While the soft spot can be frightening to some parents, it fulfills two very important functions: It allows for the extremely rapid growth of the brain, and it serves as part of the skull's shock-absorption system for all the tumbles and falls that babies inevitably take.