Flat head syndrome is a condition where a baby’s skull develops a flattened spot, usually on the back or one side of the head. It happens because infant skulls are soft and moldable, and prolonged pressure in one position can reshape the bone. Up to 20% of infants develop some degree of positional head flattening, with one study finding prevalence as high as 46% by seven months of age. The vast majority of cases are harmless and improve on their own or with simple changes at home.
Types of Flat Head Syndrome
The medical term for flat head syndrome is positional plagiocephaly, and it comes in a few distinct forms depending on where the flattening occurs.
Positional plagiocephaly is the most common type. One side of the back of the head flattens, making the head look like a parallelogram when viewed from above. You may also notice that one ear appears pushed forward, one cheek looks fuller, or the forehead bulges slightly on the flattened side.
Brachycephaly is flattening across the entire back of the head, giving the skull a wider, shorter appearance from front to back.
Scaphocephaly is the opposite pattern: the head becomes long and narrow, usually from side-to-side pressure rather than back pressure.
What Causes It
A baby’s skull bones are thin and flexible during the first several months of life, which allows the brain to grow rapidly. That same flexibility means the skull can be reshaped by outside pressure. The most common causes are straightforward.
Back sleeping. Since safe-sleep guidelines recommend placing babies on their backs, the back of the skull bears most of the contact pressure during sleep. Babies who stay in one position without being moved, or who spend extended time in car seats and bouncers, are more likely to develop flattening.
Muscular torticollis. Some babies are born with tightness in one of the neck muscles that runs from the collarbone to behind the ear. This tightness makes the baby strongly prefer turning their head to one side, concentrating pressure on the same spot every time they lie down. Torticollis is one of the most common drivers of asymmetric flattening.
Crowding before birth. Babies who were cramped in the uterus, including twins and other multiples, sometimes arrive with flattening already present from sustained pressure during the final weeks of pregnancy.
Flat Head Syndrome vs. Craniosynostosis
Not all unusual head shapes are positional. Craniosynostosis is a different condition where the bony plates of the skull fuse together too early, restricting how the head can grow. It requires surgical treatment. Positional flattening is caused by external pressure on a normal, flexible skull. Craniosynostosis is an internal structural problem with the skull itself.
A doctor can usually tell the difference through a physical exam. In craniosynostosis, you can often feel a hard ridge along the fused suture line, and the soft spots (fontanelles) on the baby’s head may feel closed or unusually small. In positional plagiocephaly, the sutures are open and the fontanelles feel normal. If there’s any uncertainty, imaging confirms the diagnosis. This distinction matters because the treatments are completely different.
How It’s Treated
Most mild cases resolve with repositioning alone, meaning you change how and where your baby rests their head throughout the day. If your baby tends to look one direction, place them in the crib so they have to turn the other way to see you. Alternate which arm you use for feeding. Limit time in car seats and swings when the baby isn’t traveling.
Tummy Time
Supervised tummy time is one of the simplest and most effective tools. You can start the day your baby comes home from the hospital, beginning with two to three short sessions of three to five minutes each day. By around seven weeks, the goal is 15 to 30 minutes of total tummy time daily. Beyond preventing flattening, tummy time builds the neck, shoulder, and core strength babies need for rolling, crawling, and sitting.
Stretching for Torticollis
When torticollis is involved, gentle stretching exercises help loosen and lengthen the tight neck muscle. A pediatrician or physical therapist will show you how to do these at home. The basic approach involves laying the baby on their back and slowly tilting the head toward the opposite shoulder, holding for about 30 seconds or until the baby resists. These stretches work well during diaper changes, after baths, or during playtime. Light massage of the neck and back muscles can also help. The key is to be gentle and never force a stretch.
Some families also work with an osteopathic physician who uses hands-on techniques to release tightness where the neck muscles attach at the base of the skull. Physical therapy referrals are common and typically very effective for torticollis.
Helmet Therapy
For moderate to severe cases, a cranial remolding helmet (also called a cranial orthosis) may be recommended. These custom-fitted helmets work by leaving space where the skull needs to grow while gently redirecting growth away from the areas that are already prominent. Severity is often measured by the difference in millimeters between the two sides of the skull: 5 to 9 mm is considered mild, 10 to 15 mm moderate, and 20 mm or greater severe. Treatment is generally considered when asymmetry reaches 10 mm or more.
Timing matters significantly. Helmets are most effective when started before six months of age, while the skull is still growing rapidly in all directions. Babies who begin helmet therapy after six months show measurably less improvement. Most babies wear the helmet for two to four months, typically 23 hours a day, removing it only for bathing.
Products to Avoid
A number of pillows, wedges, and sleep positioners are marketed to parents as ways to prevent flat head syndrome. The FDA has issued clear warnings against all of these products. Infant sleep positioners have been linked to multiple suffocation deaths, as babies can roll into positions that block their airway. These products pose a suffocation risk whether or not they make medical claims, and the FDA discourages purchasing any of them. A firm, flat sleep surface with no loose bedding remains the safest option.
Long-Term Outlook
Positional plagiocephaly is a cosmetic issue, not a brain development issue. The flattening affects the shape of the skull, not the brain inside it. Most mild to moderate cases improve substantially on their own as babies gain head control, start sitting up, and spend less time lying in one position. By 18 to 24 months, many children’s heads have rounded out noticeably even without any intervention.
This is an important distinction from craniosynostosis, which can affect brain growth and has been associated with cognitive and motor difficulties in some children. Positional flattening does not carry those same risks. For parents who are concerned, the practical steps are simple: prioritize tummy time, vary your baby’s position throughout the day, and bring up any head shape concerns at well-child visits so your pediatrician can track changes over time.