Positional plagiocephaly is a flattening on one side of an infant’s skull caused by repeated pressure on that area. It’s one of the most common findings in young babies, affecting nearly 47% of infants between 7 and 12 weeks of age to some degree. Unlike conditions where skull bones fuse too early, positional plagiocephaly involves no abnormality of the skull itself. The bones are normal and the sutures between them remain open. The shape change comes entirely from external pressure on a skull that is still soft and moldable.
How the Flattening Develops
Infant skulls are designed to be flexible. The bones haven’t fully hardened, and the joints between them (sutures) are fluid enough to allow the head to compress during birth. That same flexibility makes the skull vulnerable to sustained pressure in the weeks and months afterward. When a baby consistently rests with the same part of the head against a mattress, car seat, or swing, that area gradually flattens.
Once a flat spot forms, it tends to get worse on its own. The baby’s head naturally rolls toward the flat area because it’s the most stable resting position, and gravity holds it there. Over time, the skull can take on a parallelogram shape, where the flattened side pushes the ear and forehead on that side slightly forward. In more pronounced cases, this creates visible facial asymmetry, with one eye appearing slightly more open or one cheek looking fuller than the other.
Common Causes and Risk Factors
The single biggest driver is limited head movement during early infancy. When babies can’t or don’t turn their heads equally in both directions, one spot absorbs most of the pressure. Several things contribute to this:
- Congenital muscular torticollis: A tightness in one of the neck muscles that makes the baby strongly prefer turning to one side. This is the most well-documented contributor because it creates a consistent, repetitive head position.
- Premature birth: Preemies spend extended time in the NICU with limited repositioning, and their skulls are even softer than full-term babies.
- Multiple births: Twins and triplets face more crowding in the womb, which can create pressure on the skull before birth.
- Assisted delivery: Vacuum or forceps deliveries apply focused pressure during birth.
- Firstborn status: First pregnancies tend to have a tighter uterine environment.
Spending too much time in car seats, bouncers, and swings outside of travel also increases risk, because these devices hold the back of the head against a firm surface with little room for movement.
How It Differs From Craniosynostosis
The critical distinction parents and doctors need to make is between positional plagiocephaly and craniosynostosis, a condition where one or more skull sutures fuse prematurely. Both can cause an asymmetric head shape, but they require very different management. Craniosynostosis typically needs surgery; positional plagiocephaly does not.
The shape of the head is the most reliable visual clue. Positional plagiocephaly produces a parallelogram shape when viewed from above: the forehead and ear on the flat side shift forward together. Craniosynostosis affecting the back of the skull creates a trapezoidal shape instead. Doctors also look for a bony bulge behind the ear and a tilt of the skull base, both of which point toward craniosynostosis rather than positional flattening. Your pediatrician can usually tell the difference with a physical exam, though imaging is sometimes used to confirm.
Severity Levels
Doctors measure severity using a ratio called the Cranial Vault Asymmetry Index, which compares diagonal measurements across the skull. A difference under 3.5% is considered normal. Mild plagiocephaly falls between 3.5% and 6.9%, moderate between 7% and 9.9%, severe between 10% and 13.9%, and anything at 14% or above is classified as very severe. Most cases detected at well-child visits fall in the mild to moderate range, and these numbers help guide whether conservative treatment alone is sufficient or whether a helmet should be considered.
Repositioning and Physical Therapy
For most babies, the first line of treatment is repositioning, and it works well when started early. One study found that 77% of infants managed conservatively with repositioning alone achieved complete correction, and the overall correction rate including other conservative methods reached nearly 93%.
The basic strategy is straightforward: place the baby to sleep with the rounded side of the head resting against the mattress so that pressure shifts away from the flat spot. You can also change the orientation of the crib in the room so your baby naturally looks away from the flattened side to see you or the doorway. During the day, limit time in car seats and swings to actual car travel.
If torticollis is contributing, gentle neck stretches become part of the routine. These are simple enough to do at every diaper change. You rotate the baby’s chin gently toward each shoulder, holding for about 10 seconds per side, then tilt the ear toward each shoulder with the same hold. Three repetitions per exercise, several times a day. A pediatric physical therapist can demonstrate the technique and monitor progress.
Most infants show noticeable improvement within two to three months of consistent repositioning.
Tummy Time as Prevention
Supervised tummy time is the single most effective way to prevent positional plagiocephaly. It takes pressure off the back of the skull entirely and also builds the neck and shoulder strength babies need for rolling and crawling. The American Academy of Pediatrics recommends at least 30 to 60 minutes of tummy time per day while the baby is awake and supervised.
That doesn’t need to happen in one stretch. Starting with two or three sessions of 3 to 5 minutes works well for newborns, building up to 15 to 30 minutes of total daily tummy time by around 2 months. Alternating which direction your baby’s head faces during sleep, starting from the very first night home, also helps distribute pressure evenly across the skull.
When Helmet Therapy Is Considered
If repositioning and physical therapy don’t produce improvement after two to three months, or if the asymmetry is moderate to severe, a cranial orthotic (helmet) may be recommended. The helmet works by leaving space over the flat area while applying gentle contact on the fuller side, guiding growth into a more symmetrical shape.
Timing matters significantly. Research comparing infants who started helmet therapy at 5 to 6 months versus 7 to 9 months found that the earlier group achieved a 75% improvement in asymmetry compared to 61% in the later group. The earlier group also finished treatment faster (14 weeks versus 18 weeks) and were more likely to reach a fully normal skull shape. By around 12 months, the skull bones have hardened enough that helmet therapy becomes much less effective.
This means that a “wait and see” approach can sometimes backfire. If a baby has moderate or severe flattening at 4 months and isn’t improving with repositioning, the AAP recommends referral to a specialist by 4 to 6 months of age so the window for effective helmet therapy isn’t missed.
Long-Term Outlook
The cosmetic flattening itself is not dangerous and does not put pressure on the brain or restrict brain growth. Many mild cases resolve on their own as babies gain head control and spend less time on their backs. For moderate and severe cases that are treated, the prognosis for achieving a normal or near-normal head shape is very good, especially with early intervention.
There is, however, an association worth knowing about. A long-term follow-up study found that 39.7% of children who had persistent positional plagiocephaly received some form of special assistance in primary school, including speech therapy, occupational therapy, or special education support. Among their unaffected siblings, only 7.7% needed similar services. This doesn’t mean plagiocephaly causes developmental delays. It may instead be a marker for other underlying factors, such as limited movement in infancy, that independently affect development. Either way, it suggests that babies with noticeable plagiocephaly benefit from developmental monitoring as they grow, not just attention to head shape.