Flat head in babies: the helmet worked no better than time in a trial

Positional flat head — plagiocephaly — is one of the most common things parents are told to worry about in the first months, and in the only randomised trial to test the standard fix, a moulding helmet did no better than simply letting the condition run its course [s1]. It is also far more common, and far milder, than the alarm around it suggests: in a population study nearly half of two-month-olds had some degree of it, and the large majority were mild [s2]. Those two facts together are the case for patience over hardware.

How common, and how serious

A prospective cohort study of 440 healthy full-term infants in Calgary estimated the incidence of positional plagiocephaly at 46.6% among babies aged 7 to 12 weeks [s2]. Crucially, 78.3% of the affected infants had only a mild form, and the deformity was most often on the right side [s2]. Positional flat head is a moulding of a soft skull from lying in one position, not a problem with the brain or the bones fusing, and it tends to improve as a baby gains head control, spends less time lying down and moves more. It is common enough to be considered a normal variant of early development in most cases, which is the frame the numbers support and the marketing around helmets does not.

What the helmet trial found

The pivotal evidence is the HEADS trial, a single-blind randomised controlled trial that enrolled 84 infants aged 5 to 6 months with moderate to severe skull deformation and assigned them either to six months of helmet therapy (42 infants) or to the natural course of the condition (42 infants) [s1]. At 24 months, the change in skull shape was essentially identical between the groups: the mean difference was −0.2 for plagiocephaly (95% confidence interval −1.6 to 1.2) and 0.2 for brachycephaly, or flattening across the back (95% confidence interval −1.7 to 2.2) [s1]. Full recovery was reached in 26% of the helmet group and 23% of the natural-course group, a difference well within chance (odds ratio 1.2, 95% confidence interval 0.4 to 3.3) [s1].

What was not equal was the burden. Every parent in the helmet group reported one or more side effects — skin irritation, sweating, smell, pain, and the sense that the helmet hindered cuddling [s1]. Weighing equal effectiveness against universal side effects and substantial cost, the trial's authors explicitly discouraged the use of a helmet as standard treatment for healthy infants with moderate to severe deformation [s1].

Why guidance still lands on repositioning

The wider literature is more mixed than the single trial, and honesty requires saying so. A systematic review by the Congress of Neurological Surgeons — which noted that plagiocephaly is one of the most common reasons for paediatric neurosurgical consultation — found 3 randomised trials, 1 prospective cohort and 6 retrospective cohort studies, and reported that 5 of the 7 cohort studies comparing repositioning with a helmet found helmets corrected the shape faster [s3]. But those are lower-quality observational comparisons; the highest-quality evidence, a randomised trial, found no advantage [s1][s3]. The review's own conclusion was that repositioning education is effective in affording some degree of correction in virtually all infants with the condition [s3].

Repositioning is the low-tech version of what the helmet is trying to do: varying which way a baby's head rests, encouraging supervised tummy time while awake, and alternating positions during feeds and play. It is also why the condition is not a reason to change safe-sleep practice — see safe infant sleep and SIDS risk — since the answer is to vary head position while awake, not to move a baby off their back at night.

How to read this

Flat head is common, usually mild, and usually improves on its own, and the intervention parents are most often steered toward has not beaten time in a randomised trial [s1][s2]. That does not make helmets never useful — severe or asymmetric cases, or those with an underlying muscular cause such as torticollis, are assessed individually — but it does move the default from "treat" to "reposition and watch," which is where most of the evidence points [s1][s3]. As with much of early development, the honest reassurance is that a lot of what looks abnormal at two months is within the range of normal variation, a theme explored in child development milestones.

This article is informational and not medical advice; concerns about a baby's head shape should be assessed by a qualified clinician.