A flat spot on your baby’s head usually becomes visible between 6 and 8 weeks of age. It’s one of the most common infant skull conditions, and in most cases it’s positional, meaning it developed from external pressure rather than a problem with how the skull bones are fusing. Knowing what to look for early gives you the best chance of correcting it with simple changes at home.
What a Flat Head Looks Like
The most obvious sign is a flattened area on one side of the back of the head, or across the entire back of the head. But flattening rarely happens in isolation. When one part of the skull gets pushed in, the soft bone shifts in other directions too, creating a set of related changes you can spot if you know where to look.
Pick your baby up and look straight down at the top of their head. A symmetrical head will look like an even oval. A head with positional flattening (called plagiocephaly when it’s on one side) will look like a parallelogram: the ear, cheek, and forehead on the flattened side may appear pushed forward compared to the other side. You might also notice that one ear sits slightly farther forward than the other, or that one cheek looks fuller.
If the flattening is across the entire back of the head rather than just one side, the head may look unusually wide when viewed from above, with a shorter front-to-back length. This pattern is called brachycephaly. Some babies have a combination of both.
A few other things to watch for:
- A bald or worn patch on the flattened area, caused by repeated friction against the mattress or car seat
- A head tilt or strong side preference where your baby always turns their head the same direction, which can signal tight neck muscles (torticollis) driving the flattening
- Uneven facial features like one eye appearing slightly smaller or one side of the jaw looking fuller than the other
How to Check at Home
The bird’s-eye view is the single most useful check. Hold your baby on your lap facing away from you, or have someone hold them, and look directly down at the crown of their head. Compare the left and right sides. Are the ears lined up, or is one pushed forward? Does the back of the head curve evenly, or is there a clear flat zone?
You can also lay your baby on a flat surface and look at their head from behind. If the head consistently rocks to one side rather than resting centered, that can indicate asymmetry. Taking photos from directly above every few weeks gives you a visual record that makes subtle changes easier to track. It’s often hard to notice gradual flattening when you see your baby every day, so photos taken a few weeks apart can be revealing.
Mild vs. Moderate vs. Severe
Doctors measure flat head severity by comparing the diagonal dimensions of the skull. The difference between the two diagonals, expressed in millimeters, determines the category. A difference under 5 millimeters is considered normal. Mild plagiocephaly falls between 5 and 10 millimeters. Moderate is greater than 10 up to 15 millimeters, and severe is anything above 15 millimeters.
At home, you won’t be able to measure millimeters precisely, but you can gauge severity visually. If the asymmetry is only noticeable when you deliberately look from above, it’s likely mild. If you can see the unevenness from across the room, or if facial features look noticeably different on each side, the flattening may be moderate or severe and worth bringing up with your pediatrician sooner rather than later.
Why Timing Matters
A baby’s skull bones are soft and separated by flexible gaps during the first several months of life. This is what allows flattening to happen, but it’s also what allows the head to round back out. Repositioning techniques, where you change how your baby is positioned during sleep and awake time, work best before 4 months of age, while the skull is still highly moldable.
After about 4 months, the bones gradually become firmer. That doesn’t mean correction is impossible, but it becomes slower and may require more intervention. If a helmet (cranial remolding orthosis) is needed, it’s typically prescribed before 12 months of age. The average helmet treatment lasts about three months, though this varies based on the baby’s age when treatment starts and how significant the flattening is. Younger babies tend to respond faster because their skulls are still growing rapidly.
What Causes Positional Flattening
Back sleeping is the biggest contributor, and it’s still the safest sleep position for reducing the risk of SIDS. The tradeoff is that babies who spend many hours on their backs, between nighttime sleep, car seats, bouncers, and swings, can develop a flat spot from sustained pressure on the same part of the skull.
Torticollis, a tightness in one of the neck muscles, makes flattening worse because the baby strongly prefers turning their head to one side. If your baby almost always looks the same direction, mention it to your pediatrician. Treating the neck tightness (usually with gentle stretching exercises or physical therapy) is often the first step in addressing the head shape, because the flattening will keep progressing if the positional preference isn’t resolved.
Premature babies are at higher risk because their skulls are softer at birth, and they often spend extended time in one position in the NICU. Multiples (twins, triplets) also have higher rates due to cramped positioning in the womb.
Steps That Help Reverse Mild Flattening
Tummy time is the most effective daily habit for both preventing and improving a flat spot. The NIH recommends two or three short sessions of 3 to 5 minutes each day for newborns, building up to 15 to 30 minutes of total daily tummy time by around 2 months of age. Tummy time takes pressure off the back of the skull and strengthens the neck and shoulder muscles that help your baby eventually control their own head position.
Beyond tummy time, simple repositioning makes a real difference:
- Alternate the head direction at sleep time. Place your baby with their head at one end of the crib one night, then the other end the next. Babies tend to turn toward the room or light source, so this naturally shifts which side of the head bears weight.
- Limit time in containers. Car seats, swings, and bouncers all press on the same spot. Use them when needed, but give your baby time on a flat surface or in your arms between uses.
- Encourage your baby to look the other way. During feeding, playtime, and diaper changes, position yourself or toys on the side your baby tends to ignore. This gently trains them to turn their head in both directions.
For mild cases caught early, these changes alone often produce noticeable improvement within a few weeks. Moderate to severe cases, or cases where repositioning hasn’t helped by around 5 to 6 months, may be evaluated for helmet therapy. A pediatrician or pediatric craniofacial specialist can take precise measurements and recommend next steps based on your baby’s age and the degree of asymmetry.
Flat Head vs. Craniosynostosis
Positional flattening is by far the more common cause of an abnormal head shape, but there is a rarer condition called craniosynostosis where one or more of the skull’s natural seams fuse too early. This creates a rigid, abnormal shape that won’t improve with repositioning.
The key difference is that craniosynostosis produces a hard, ridged line along the fused seam, and the shape abnormality tends to look different from typical positional flattening. A positional flat spot feels smooth and the skull remains flexible, while craniosynostosis creates a firm ridge you can sometimes feel with your fingers. Craniosynostosis also tends to get progressively worse rather than improving with repositioning. If your pediatrician suspects it, imaging can confirm the diagnosis. It requires surgical correction, but the positional flat head that the vast majority of parents are noticing does not.