Cranial asymmetry, often called flat head syndrome, describes an unevenness or flattening of the baby’s skull that develops after birth. The two most common forms are positional plagiocephaly, a flattening on one side of the back of the head, and brachycephaly, a symmetrical flattening across the entire back of the head. Since an infant’s skull bones are soft and malleable, they are susceptible to molding from consistent external pressure, making this a frequently observed issue in the first few months of life.
Understanding Positional Cranial Asymmetry
Positional asymmetry results from the prolonged application of external force on the same area of the soft, growing skull. Because infants spend many hours sleeping on their backs, the constant pressure of the mattress can cause the skull to flatten at the contact point. This condition is classified as deformational, meaning it is caused by positioning, and is distinct from craniosynostosis, where the skull’s sutures fuse prematurely. Positional flattening does not affect brain growth or development, though it may result in a cosmetic change to the head shape.
However, back sleeping alone is not a corrective measure for an established flat spot and may instead maintain or worsen the flattening. When a flat spot is already present, the head naturally rests on that flat area. A pre-existing preference to turn the head to one side, perhaps due to a tight neck muscle known as congenital muscular torticollis, can also contribute to a persistent flat spot.
Safe Sleep Priority and Head Shape
The back-to-sleep position is the universally recommended standard for infant sleep safety, despite its association with an increase in positional head flattening. This recommendation is based on a substantial reduction in the incidence of Sudden Infant Death Syndrome (SIDS) since the “Back to Sleep” campaign was introduced. Placing a baby to sleep on their back is the most effective measure to mitigate this risk.
The health benefit of reducing SIDS risk significantly outweighs the risk of developing a mild head flattening. Parents must continue to place their infants on their backs for all sleep times, including naps and overnight. The focus then shifts to proactive measures during waking hours to counteract the pressure on the back of the head that occurs during sleep.
Active Repositioning and Corrective Measures
Since back sleeping is mandatory for safety, the correction of cranial asymmetry relies on actively changing the pressure points when the baby is awake and supervised. The most important activity is supervised “Tummy Time,” which relieves pressure from the back of the head and strengthens neck, shoulder, and arm muscles. Tummy Time should be practiced several times a day for short periods when the baby is alert, starting in the first few weeks of life.
Repositioning techniques during waking hours are highly effective for mild cases, particularly for plagiocephaly. This involves consciously altering how the baby is held, fed, and stimulated to encourage them to turn their head away from the flattened side. Parents can change the direction the baby faces in the crib or place toys so the baby must look toward the unflattened side of their head. Limiting the time a baby spends lying on their back in carriers, car seats, or swings is also recommended, as these devices apply pressure to the back of the head.
If a baby consistently holds their head to one side or if repositioning efforts do not show improvement, it may indicate underlying torticollis, which requires a consultation with a pediatrician or physical therapist. For moderate to severe cases that do not respond sufficiently to repositioning by about six months of age, a cranial orthotic device, commonly called a helmet, may be recommended. These custom-fitted helmets gently redirect the skull’s growth into a more rounded shape by applying pressure to the protruding areas.