For nearly three decades, back sleeping has been recommended as the safest position for infants. However, one of the adverse side effects is head flattening. Conservative estimates suggest that 25-40% of infants who sleep on their backs will develop some degree of asymmetrical (plagiocephaly) or symmetrical (brachycephaly) head flattening. These changes occur when an infant’s rapidly growing head tries to expand against a flat mattress, car seat, or other resting surface. Contrary to popular belief, this process has nothing to do with a "soft" head or malleable bones. It is exclusively a result of growth displacement around a point of contact.
