Since the Back to Sleep campaign began in the early 1990s, sudden infant death has fallen dramatically. It is one of the most successful public health interventions in paediatrics. It also produced a side effect nobody minds very much but every parent notices: more babies with a flattened area on the head.

The medical name is positional plagiocephaly. It is common — depending on how it is measured, somewhere between one in five and nearly half of infants have some degree of it — and in the overwhelming majority of cases it corrects itself.

What it is, and what it is not

Positional plagiocephaly is a flattening caused by pressure. A baby's skull is soft and designed to be, and a head that rests in the same position for many hours takes on that shape. It is a moulding of a normal skull.

It is not craniosynostosis, which is a rare condition where the joints between the skull bones fuse too early. That requires surgical assessment and looks different — a ridge along the fused joint, a head shape that is getting worse rather than better, and often a smaller than expected head circumference. If there is any doubt, this is a paediatrician's question, not a chiropractor's.

Why the neck matters

Plagiocephaly rarely arrives on its own. A baby who always turns the same way develops flattening on that side, and the reason they always turn the same way is often a limitation in the neck.

Congenital muscular torticollis — tightness in the sternocleidomastoid muscle on one side — occurs in roughly one in every 250 births and is strongly associated with head shape asymmetry. This is where a physical assessment genuinely earns its place: if a baby cannot comfortably turn both ways, repositioning advice alone will not work, because the baby will keep returning to the side that is comfortable.

Treating the restriction and the position together is the approach with the best support behind it, and it is usually a collaboration — a physiotherapist, a chiropractor, and a paediatrician if the asymmetry is significant.

What actually helps

  • Tummy time, from the first weeks. Short and frequent beats long and rare — a few minutes several times a day, always supervised and always while awake. It is the single most effective thing you can do.
  • Alternate the head end of the cot. Babies turn towards the light and the door. Swapping which end they sleep at swaps which way they turn.
  • Change your carrying and feeding sides. Most of us have a dominant side and use it without noticing.
  • Limit time in car seats, bouncers and swings outside of travel. Every hour in a moulded seat is an hour of pressure on the same spot.

Babies still sleep on their backs. That rule does not change, and no head shape concern is a reason to change it.

Timing, and helmets

The skull is most responsive in the first six months, which is why early attention is worth more than later intervention. Most positional flattening improves markedly once a baby is sitting, crawling and spending far less time lying down.

Helmet therapy is a reasonable option in a minority of cases — significant asymmetry, a baby past the age where repositioning alone is likely to work. It is also expensive, demanding for the family, and a large randomised trial found no meaningful difference against natural recovery in moderate cases. It deserves a careful discussion, not a quick recommendation.

What to ask for

A useful assessment includes measurement rather than impression — the same measurement repeated over time is what tells you whether anything is changing. Ask what was measured, what the number was, and when it will be checked again.

And ask about the neck. A head shape assessment that never examined how far your baby can turn has missed the part that is most likely to be doing something about it.