When should I worry about my baby's flat head?

Flat spots are common, affecting around one in five babies at four months, and most are positional. What is worth understanding is that a flat spot does not fill back in. Once your baby can move their own head the pressure comes off and the flattening stops getting worse, but nothing pushes the flat area out again and the head grows on around it. The things that genuinely warrant concern are different: a head shape that looked unusual from birth, one that is getting worse rather than better, one that does not respond to changes in position at all, or any developmental concern alongside it. Those need a GP or paediatrician rather than watching and waiting.

If you have noticed something and cannot settle about it, you are not overreacting. Flat spots come up often at child and family health nurse visits, and noticing early gives you more options. This page covers how common it is, why it happens, what actually happens next, and the specific signs that mean something other than positional flattening.

Common enough that you are almost certainly not the only one in your mothers' group wondering. Hutchison and colleagues followed 200 New Zealand infants from birth and found flattening in around one in five at four months. The NSW Health guideline for allied health professionals puts prevalence at 22.1 per cent at seven weeks.

It is worth saying what that number is not. Fewer than a quarter of babies placed on their back develop visible flattening, so this is not an inevitable consequence of back sleeping. Most babies sleep on their back and most do not flatten.

Two things collided. From the early 1990s, health authorities worldwide began recommending babies be placed on their backs to sleep on a firm, flat surface. It worked. Sudden infant death rates fell dramatically, and it remains one of the most successful public health changes of the last few decades. Cases of head flattening however rose over the same period.

The mechanism is not that a baby's skull is soft and squashes. Dr Gary Rogers, a craniofacial surgeon at Children's Hospital Boston, points out that if softness were the cause, every back-sleeping baby would flatten. What actually happens is growth. The skull grows outward in response to the brain expanding underneath it, and where that growth meets a resting surface it is resisted, so the extra volume is displaced elsewhere. Rogers uses a pumpkin: it cannot grow into the ground, so it grows along it and flattens underneath.

That same principle, growth meeting resistance, is what happens when steady pressure lands on one part of a baby's head for months at a time. The Perfect Noggin is a contoured sleep surface designed to redistribute that pressure away from flat spots, working alongside your physiotherapist's work on any neck tightness rather than in place of it.

None of that is a reason to change how your baby sleeps. Back sleeping on a firm surface remains the safest sleep position and it is not up for negotiation because of a flat spot. Always follow current Red Nose Australia safe sleep guidance.

Certainly not, and the reason is anatomical rather than reassuring noise. In most cases there is a cervical muscle imbalance underneath it, a neck that does not turn evenly both ways. Fenton and Gaetani report congenital muscular torticollis in up to 70 to 95 per cent of infants with deformational plagiocephaly.

Here is the part most parents are never told: that imbalance usually develops before birth. When a baby's head is held rotated and tilted in the womb for long enough, one neck muscle shortens and the opposite one lengthens and weakens. So when you reposition a baby with neck tightness, the muscle pulls the head back within minutes. Parents blame themselves for not persisting. The muscle was working against them the whole time.

Partly, and it helps to know what is actually happening. A flat spot forms because steady pressure on one part of the skull holds it back while the rest of the head keeps growing. Once your baby has the head control to move themselves, that pressure comes off and the flattening stops getting worse. What it does not do is fill back in. Nothing pushes the flat area out again, so the head grows on around it.

That is why the numbers can read as more reassuring than they are. In the Hutchison cohort flattening fell from 19.7 per cent at four months to 9.2 per cent at eight months, 6.8 per cent at twelve months and 3.3 per cent by two years. Those are proportions. As the head gets bigger the same flat area becomes a smaller share of it and scores better, without the indentation itself changing. Steinbok and colleagues followed children to beyond five years of age and found residual asymmetry was noticed by 58 per cent of parents, though only 21 per cent were concerned about their child's appearance.

So the honest answer is that the appearance often improves, because growth disguises it, while the flat spot itself largely stays. How much your baby's own growth will cover it is not something anyone can predict, and by the time you know, the window where the skull is most responsive has passed. That is the argument for getting it assessed now rather than waiting: an assessment tells you which situation you are actually in.

Everything above describes positional flattening, which is what the great majority of flat spots are. Some head shapes are not positional. Craniosynostosis, where the joints between the skull bones fuse too early, produces a head shape that needs medical assessment rather than repositioning, and it should not be watched and waited out.

You do not need to push for a scan. Rogers notes a specialist can usually tell these conditions apart from history and examination. When to seek medical assessment for your baby's head shape goes through this in full.

Separately from that, it is also worth raising if your baby strongly favours one side however you reposition them. That is the neck rather than the skull, and it is the thing most likely to keep a flat spot in place. Our guide to torticollis covers what to look for.

That is a common experience, and the reassurance is often right as far as it goes. The question worth asking is a narrower one: was the neck specifically assessed, or was it a look at the head shape alone.

What a brief look does not always establish however is whether there is neck tightness underneath it, particularly early on when it can be subtle. Before three to four months a baby's head is supported by a surface most of the time, so an imbalance can be close to invisible. It shows once your baby starts holding their own head up.

So the useful question is not whether someone was concerned, it is whether the neck was specifically assessed. If it has not been, asking for a referral to a paediatric physiotherapist is a reasonable next step, and worth asking for by name.

Three things, in order. Work out what you are actually looking at, using the four-point check, which takes about two minutes. Photograph your baby's head from directly above every two weeks, in the same spot and the same light, because change is invisible day to day and obvious across a month. And book a paediatric physiotherapy assessment, particularly if there is any side preference.

In the meantime, what you can do at home sets out the positioning changes and tummy time that help, and our timing guide covers what is realistic at your baby's age.

This article is for educational purposes and is not a clinical assessment or medical advice. A paediatric physiotherapist, child and family health nurse, GP or paediatrician can assess your baby's head shape properly and advise on the right approach for your family.