What causes a baby's head shape to appear uneven?

Sometimes a baby's head is molded unevenly while passing through the birth canal. In other cases, head shape changes after birth as a result of pressure on the back of the head when the baby lies on his or her back.

You'll notice two soft areas at the top of your baby's head where the skull bones haven't yet grown together. These spots, called fontanels, allow a baby's relatively large head to move through the narrow birth canal. They also accommodate your baby's rapidly growing brain during infancy.

Because your baby's skull is malleable, however, a tendency to rest the head in the same position can result in an uneven head shape well past the time when birth-related lopsidedness evens out. This is known as positional plagiocephaly.