Dr. Greene's Answer
There are several reasons for one side of the head to be flat. The most common is positional plagiocephaly, where it flattens from sleeping on the same side and spending a lot of time lying down. This is not a serious problem and it will usually correct itself over time.
You might speed this up by alternating the end of the crib where you put her head so she will be motivated to look more in both directions. Kids often spend a lot of time looking toward the door or whatever is most interesting in the room.
“Tummy time” is another useful strategy to prevent the progression of this condition. When your infant is awake, make sure she spends some time lying on her stomach (while supervised)This position not only takes pressure off the head, but also helps develop the muscles of the neck and shoulders.
Rarely, the head will be flat in one area because the suture lines between two of the skull’s bony plates have grown together. This is a different condition called craniosynostosis and this one does not improve on its own.