Many parents notice that their baby's head develops a flat patch on one side or at the back, particularly in the early months. The back-to-sleep guidance that has prevented thousands of sudden infant deaths has the side effect of increasing the time babies spend lying on the same area of skull, and the infant skull is soft and mouldable. For most babies the flattening is mild and improves naturally as the baby gains head control and spends more time upright.
For a smaller number, the flattening is significant enough to benefit from active repositioning or, in more marked cases, helmet therapy. Recognising which situation a baby is in and what to do about it is what parents need.
Healthbooq (healthbooq.com) covers newborn and infant health through the early months.
What Causes It
The infant skull is made of several separate bone plates that are not yet fused, connected by flexible sutures. This allows the head to pass through the birth canal and allows the brain to grow rapidly in the first years. It also means that sustained pressure on one area causes that area to flatten.
Positional plagiocephaly is the most common type. A flat area on one side of the back of the head is the typical pattern, often with the ear on the affected side pushed slightly forward. It develops when the baby consistently turns their head to one side while lying on their back, creating sustained pressure on that area.
This is frequently associated with torticollis, a tightness of the sternocleidomastoid muscle on one side of the neck that makes turning the head in one direction easier than the other. When torticollis is present, repositioning strategies are less effective until the neck tightness is also treated, usually with physiotherapy or stretching exercises.
Back sleeping must continue: it reduces the risk of SIDS by up to 50 per cent and should never be compromised to address head shape.
Assessment
At well-baby checks, the GP or health visitor assesses head shape as part of the examination. A parent who is concerned earlier can raise it at any point.
A GP will usually check the sutures (to rule out craniosynostosis, a different condition where sutures close prematurely, causing head shape changes that need a different approach), assess whether the ears are symmetrical, check for neck tightness, and advise on repositioning strategies.
Craniosynostosis is rare but important to distinguish: it produces ridging along the fused suture and does not improve with repositioning. It may require surgical management by a specialist craniofacial team.
Prevention and Repositioning Strategies
Supervised tummy time when the baby is awake and alert is the most important measure. It eliminates pressure on the back of the skull entirely, strengthens the neck and shoulder muscles, and is essential for motor development. Beginning from birth, even short periods of tummy time on a parent's chest or a firm flat surface, building gradually as the baby tolerates it, makes a real difference.
Varying the head position during sleep: place the baby so that the preferred side is toward the wall or a less interesting direction, so they are encouraged to turn toward the room. Alternate which end of the cot the head is placed.
Reduce time in car seats, bouncers, and swings when not travelling: these tend to position the baby on the back of the skull and limit head turning. Holding and carrying alternates the position.
When bottle feeding, alternate which arm holds the baby, and position feeds so the baby turns their head to the non-preferred side.
Osteopathy and chiropractic for plagiocephaly are sometimes sought by parents. The evidence for these is not strong, and they are not recommended by NHS guidance. Repositioning and physiotherapy (when torticollis is present) have better evidence.
Helmet Therapy
Helmet therapy (cranial orthosis) involves a custom-made plastic helmet worn for 23 hours a day over several months. It creates a space over the flattened area and applies gentle pressure to the rounded areas, guiding skull growth into a more symmetrical shape.
The optimal window is approximately five to twelve months. Before five months the skull is very mouldable but the helmet cannot be fitted reliably. After twelve months, skull growth slows and the response to helmet therapy diminishes.
On the NHS, helmet therapy is not routinely funded and access varies considerably by area. The 2020 NHS England guidance found insufficient evidence to support routine referral but acknowledged that moderate to severe cases may benefit. Most families who pursue helmet therapy do so privately, with costs of several thousand pounds. Some European countries fund this routinely through state healthcare.
Specialist teams that assess and fit helmets include both NHS craniofacial services and private providers. A referral from a GP or paediatrician to a specialist is the starting point.
What "Significant" Looks Like
Most cases are mild and resolve with repositioning before twelve months. More significant cases have visible asymmetry, particularly when viewed from above or from the front, with the affected ear visibly forward of the other.
Formal scoring systems (such as the Cranial Vault Asymmetry Index) are used by specialists to categorise severity. Parents can get a free assessment at some specialist services, which helps determine whether active treatment is likely to benefit.
Key Takeaways
Positional plagiocephaly (a flattened area on one part of the skull) has increased since the 1990s safe sleep campaigns successfully promoted back sleeping, which is still the correct recommendation. The head shape is usually not a sign of brain problems and often improves with repositioning strategies: supervised tummy time when awake, varying the side the baby turns their head to sleep, and alternating which arm is used to carry the baby. Helmet therapy (cranial orthosis) may be recommended for moderate to severe cases that do not respond to repositioning and is most effective between five and twelve months when skull growth is most rapid. Torticollis (tightness of the neck muscle) frequently coexists with plagiocephaly and should be treated alongside.
