What Causes Plagiocephaly?
(Flat Head Syndrome)
If you’ve noticed a flat spot on the back or side of your baby’s head, you’re not alone. This condition—called plagiocephaly, or more generally flat head syndrome—has become increasingly common in recent decades. But what causes plagiocephaly? And more importantly, what can you do about it?
On this page, we’ll walk through the science behind baby head flattening, the role of neck tightness and sleep position, and how to spot early warning signs so you can act fast.
What Is Plagiocephaly?
Plagiocephaly refers to an asymmetrical flattening of the skull, usually on the back or one side of a baby’s head. When the flattening is more symmetrical across the back, it’s known as brachycephaly.
The root cause? Pressure. A baby’s head grows rapidly in the first few months of life, and if that growth is met with consistent pressure in one area—like from lying in the same position for hours against a firm, flat surface—the head shape can start to flatten.
Why Does Flat Head Syndrome Happen?
1
Back-Sleeping Is Safer—But It Comes with Side Effects
Ever since the “Back to Sleep” campaign began in the 1990s to reduce the risk of SIDS (Sudden Infant Death Syndrome), parents have rightly been encouraged to put babies on their backs when they sleep. However, this life-saving recommendation has had an unintended side effect: up to 40% of babies now develop some degree of head flattening.
2
Pressure + Growth = Flattening
The infant cranium is fast-growing and this growth meets resistance, like resting on the same part of a flat mattress, swing, or car seat, pressure displaces growth away from the area of contact. Similar to a pumpkin flattening as it grows against the ground- it starts off round and gradually becomes flatter as it grows.
3
It's Not About Soft Heads
Contrary to popular belief, plagiocephaly is not caused by soft skull bones. The flattening occurs due to external forces acting during a period of rapid skull growth, not because a baby’s head is unusually malleable. If a soft skull were the only problem, virtually every child would be affected and one would see the head flatten immediately once an infant is placed on any flat surface. This does not occur.
The Role of Torticollis in Head Flattening
One of the most common causes of plagiocephaly is a condition called congenital muscular torticollis (CMT). This is when a tight or shortened neck muscle causes the baby to turn their head in one preferred direction—often the same direction every time they sleep. If your baby consistently turns their head one way when lying down, they’re much more likely to develop flattening on that side. Other less common causes of flattening are prematurity, developmental delay, and iatrogenic causes (hospitalization).
When Does Plagiocephaly Develop?
Most flattening becomes noticeable between 6–8 weeks of age, especially in babies who lie still for long periods. Without intervention, the flattening can worsen until around 4–5 months, when most babies gain head control and move more independently.
After this point, the shape may improve naturally—but some asymmetry or flattening can persist into adulthood if not addressed early.
Why Repositioning and Tummy Time Don't Always Work
Many parents are told to try tummy time, head turning exercises, and repositioning techniques to reduce pressure on one side of the baby’s head. And while these strategies can be marginally effective, they don’t work for every baby—especially those with more significant flattening, or infants who have a predisposing risk factor such as congential muscular torticollis, prematurity, or developmental delay.
If these measures aren’t helping, you are not alone. Most parents try desperately to avoid head flattening and, despite their best efforts, their baby's head continues to flatten. In many cases, traditional advice isn’t enough.
Hidden Torticollis:
Why It’s Often Missed
Unfortunately, many cases of torticollis go unnoticed. Pediatricians and physical therapists often rely on very specific signs—like a clear head tilt and limited passive range of motion. But subtle torticollis can still cause big problems, and may show up as:
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A strong, consistent head-turning preference
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Asymmetry in movement
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Delayed motor milestones
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Flattening despite repositioning efforts
If your baby always looks the same direction in photos—or always turns to the same side when lying down—this is worth bringing up with your pediatrician or a specialist.
How to Prevent and Treat Plagiocephaly
The key to preventing and minimizing flat head syndrome is to change the point of pressure on the skull during the months when the head is growing most rapidly.
1
Tummy Time
Start early and increase gradually to strengthen neck muscles and encourage movement.
2
Repositioning
Alternate your baby’s head direction during sleep and feedings to relieve pressure from one spot.
3
Physical Therapy
Especially helpful for babies with torticollis or delays in motor development.
4
Sleep Surface Modification
An alternative to tedious repositioning tactics is sleep surface modification. While a flat mattress inevitably promotes head flattening, a contoured resting surface will promote a more rounded posterior head shape.
5
Professional Evaluation
A pediatric physical therapist or cranial specialist can provide personalized guidance and spot subtle issues early.
Looking for a Safe, Proven Way to Support Healthy Head Shape?
The Perfect Noggin is an anatomically shaped infant rest surface that replaces a conventional flat mattress, which can induce head flattening, with a contoured resting surface that supports normal head shape and form.
Perfect Noggin is not a pillow or repositioning device—it’s a thoughtfully engineered alternative to traditional flat surfaces, created to support your baby’s natural development during those crucial early months of life.