A “flat head” is a flattened area on a baby’s skull, most often caused by repeated pressure on the same spot during sleep or rest. The medical term is positional plagiocephaly (flattening on one side) or brachycephaly (flattening across the back). It’s remarkably common: one Canadian population study of healthy, full-term infants found that 47% of babies between 7 and 12 weeks old had some degree of positional flattening. In nearly all cases, flat head is a cosmetic issue rather than a medical one, and it improves with simple changes at home.
Why Baby Skulls Are Vulnerable to Flattening
An infant’s skull isn’t a single solid piece of bone. It’s made up of several bony plates connected by flexible joints called sutures and separated by soft spots known as fontanelles. This flexibility exists for good reason: it allows the head to pass through the birth canal and gives the brain room to grow rapidly in the first year of life. The soft spots typically close before a child’s second birthday, and most major sutures don’t fully fuse until well into adulthood.
That same flexibility means the skull is easily molded by outside pressure. When a baby spends many hours with the same part of their head resting against a mattress, car seat, or swing, the bone in that area can gradually flatten. The younger the baby, the softer the skull and the more susceptible it is to reshaping.
Common Causes and Risk Factors
Back sleeping is the single biggest contributor. Babies sleep on their backs for many hours each day (as they should, since back sleeping dramatically reduces the risk of sudden infant death). But if a baby consistently turns their head to the same side while sleeping, that section of the skull absorbs steady pressure and can flatten over weeks.
Several other factors raise the risk:
- Torticollis. Tightness in one of the neck muscles causes a baby’s head to tilt or rotate to one side. Because the baby can’t easily turn their head the other way, one spot on the skull takes all the pressure. Torticollis and flat head frequently appear together.
- Premature birth. Preemies have softer, less developed skulls and typically spend more time lying flat in the hospital and at home.
- Multiple births. Twins and triplets face cramped conditions in the womb, which can start the flattening process before birth.
- Too much time in car seats or swings. Any device where the baby’s head leans against a firm surface adds pressure, especially if used outside of car travel.
How Flat Head Differs From Craniosynostosis
Not every unusual head shape is positional. Craniosynostosis is a much rarer condition in which one or more skull sutures fuse too early, forcing the skull to grow in an abnormal pattern. The key difference: craniosynostosis is present at birth and involves bone that has already hardened along a suture line, while positional flattening develops gradually over weeks of external pressure.
A doctor can usually tell the two apart by examining the baby’s head. In positional plagiocephaly, the ear on the flat side shifts slightly forward, and the forehead on that same side may bulge a bit. In craniosynostosis, the ear shifts backward toward the fused suture, and the bulging appears on the opposite side. Sleep history also matters: if a baby has always favored one sleeping position, positional flattening is far more likely. When there’s any doubt, imaging (usually a CT scan) can confirm whether the sutures are open and healthy or prematurely fused.
Repositioning: The First Line of Treatment
Most mild to moderate flat head improves without any special equipment. The goal is simple: reduce pressure on the flat spot and encourage the baby to spend time in other positions.
Start with how you place your baby in the crib. Babies naturally want to look toward the room, a doorway, or activity. Position them so that turning toward the interesting stuff means turning away from the flat spot. Move crib toys and mobiles to the side that encourages your baby to look in the opposite direction. If the flattening is on the right, lay your baby down so they’ll want to look left.
Outside of sleep, limit time in car seats, bouncy seats, and swings. Take your baby out of the car seat as soon as you’re no longer driving, even if they’re napping. Upright seating devices are better for head shape than reclined ones where the head rests against a surface. During awake time, try side-lying play with a rolled blanket behind the shoulder and hip for support, keeping the flat spot facing up. Carrying your baby in a side-lying hold along your forearm also takes pressure off the flat area. An hour of side-lying play per day is a reasonable target for babies with noticeable flattening.
Why Tummy Time Matters
Tummy time is the single most effective prevention and treatment tool. When your baby is on their stomach, no pressure reaches the back or sides of the skull, and the neck and shoulder muscles that help with head turning get stronger.
The American Academy of Pediatrics recommends starting with 2 to 3 short sessions per day, each lasting 3 to 5 minutes, and working up to 15 to 30 minutes total by around 7 weeks of age. By 3 months, aim for a total of about an hour spread across the day. If your baby resists tummy time, there are ways to ease into it: lying tummy-to-tummy with you while you lean back, draping the baby over your lap, carrying them face-down along your forearm, or placing a small rolled towel under their chest for extra support during floor time.
When Helmet Therapy Is Considered
If repositioning and tummy time haven’t improved the shape after a few months, or if the flattening is moderate to severe, a doctor may recommend a cranial remolding helmet. The helmet works by leaving space over the flat area so the skull can grow into it, while gently preventing further growth in areas that already bulge.
Helmets work best when started before 8 months of age, when the skull is still growing rapidly and most responsive to gentle guidance. Babies referred after 8 months can still benefit, but they generally need to wear the helmet for a longer period. Treatment typically lasts several months, and some children need a second helmet if correction isn’t complete after the first.
The baby wears the helmet for most of the day and night, removing it only briefly for bathing and cleaning. Most babies adjust within a few days. The helmet itself doesn’t squeeze or force the skull into shape; it simply directs natural growth.
Physical Therapy for Torticollis
When flat head appears alongside torticollis, treating the neck tightness is essential. A pediatric physical therapist will assess the baby’s neck range of motion and any postural asymmetry, then design a plan that includes gentle stretching, positioning strategies, and a home program for parents. The stretches help lengthen the tight neck muscle so the baby can freely turn their head both ways, which removes the underlying reason one spot on the skull keeps getting all the pressure. Early referral leads to faster results, and most babies with mild torticollis respond well within a few months of consistent stretching and repositioning.
Long-Term Outlook
Positional flat head does not affect brain development. The brain grows normally beneath the flattened area. For the vast majority of babies, the shape improves significantly once they start spending more time upright, sitting, crawling, and moving through their environment. The skull continues to grow and remodel throughout early childhood, and mild flattening that’s still present at 12 months often becomes unnoticeable as the child grows and develops hair.
In more severe cases that go unaddressed, some asymmetry can persist into later childhood and adulthood. This is primarily cosmetic, potentially affecting how glasses or helmets fit, or creating visible unevenness in the forehead or ears. These outcomes are uncommon when families use repositioning techniques consistently during the first several months of life.