The flattening of a baby’s skull is caused by the pressure on the skull from a flat surface.
Up to approximately 12 months old, the skull bones of a baby are still relatively soft and are liable to become flattened against a flat surface if prolonged pressure is applied and the baby’s head is relatively still for long periods. Typically, this can occur through sleeping on a normal flat mattress.
If a baby has a preferred side to which to rotate, the head will constantly be looking to the same side thereby putting pressure on the same spot for long periods.
In the case of brachycephaly the baby is left for long periods in the face up position thereby putting pressure on the back of the head, often resulting in a flattening deformity due to the weight of the head against a flat surface. A flat mattress as well as lying a baby on his/her back on a carpet are typical causes. Semi-reclined bouncy chairs can also cause prolonged pressure on the back of a baby’s head.