The skull consists of a number of bone plates that are naturally knitted together at sutures, where the bone plates overlap. One long suture goes from back to front in the middle of the skull. Other sutures extend to the forehead, sides, and back of the skull. The body produces new bone at the suture lines. This allows the bones to grow evenly, resulting in a symmetrical head.
The top and back of a newborn’s skull are very flexible. Many cultures, including ancient Egyptians and some Native American tribes, took advantage of this flexibility to mold babies’ heads into different shapes. They did this by wrapping bands around babies’ heads or placing babies on flat headboards.
Now, some modern parents are inadvertently doing the same thing. When a baby sleeps only on his or her back with the soft, thin bones at the back of the head supporting the weight of his or her skull and brain, a similar molding of the skull can occur. This condition is known as positional molding.
Because the baby’s head is very soft in both the bone layer and brain layer, it tends to deform like a beanbag--flattening in the back and front and widening on the sides. If your baby prefers one side of the back of his or her head to the other, the skull can take on an asymmetrical, lopsided shape. If most of the flattening is in the back of his head, it may be covered by hair and barely noticeable. But if the shape of the front and sides of his or her head also are affected, parents are likely to notice and to worry.