A flat head is usually visible to the naked eye, and you can spot it by looking at your baby’s head from above, from the sides, and from behind. The flattened area might be on one side of the back of the skull, across the entire back, or even along the top. Knowing what to look for and where to look makes it straightforward to identify at home.
The Bird’s-Eye View Check
The most reliable way to assess head shape at home is to look down at your baby’s head from directly above while they sit in your lap or lie face-up. A symmetrical head will look roughly oval from this angle. If you notice that one side of the back of the head looks flatter than the other, or that the whole back of the head seems unusually straight rather than gently curved, that’s the hallmark sign of a flat spot.
In positional plagiocephaly, the most common type, the head looks like a parallelogram from above. One side of the back is flat, and the entire opposite side of the face shifts slightly forward in compensation. You’ll often notice the ear on the flat side is pushed forward compared to the other ear. From the front, one cheek or one side of the forehead may look fuller than the other, and the nose can appear slightly off-center.
If the flattening runs straight across the entire back of the head rather than favoring one side, the head will look wide and short from above. This pattern is called brachycephaly, and the back of the skull may feel almost vertical when you run your hand over it.
Signs to Look for on Each Part of the Head
- Back of the skull: A flat spot on one side, or a broad flat area across the whole back. Compare left and right by feeling with your hands.
- Ears: One ear sitting noticeably farther forward or higher than the other. This is one of the easiest asymmetries to catch.
- Forehead: One side bulging more than the other, or the forehead appearing unusually prominent on the side opposite the flat spot.
- Face: Uneven cheeks, a jaw that looks slightly crooked, or eyes that don’t appear perfectly level. Mild facial asymmetry often accompanies the skull flattening.
Different Flat Head Shapes
Not all flat heads look the same, and the shape tells you something about what’s going on.
Positional plagiocephaly is by far the most common. It develops because a baby spends a lot of time lying on one part of their skull. The head takes on that parallelogram shape, with the flat side in the back and the opposite side of the face pushed slightly forward. All the skull’s growth plates remain open and healthy. This type is not dangerous and responds well to repositioning or, in moderate to severe cases, helmet therapy.
Positional brachycephaly happens when a baby consistently lies flat on the entire back of the head. The skull becomes wide relative to its length. Clinicians define brachycephaly as a cranial index (the ratio of head width to head length) of 90% or higher.
Scaphocephaly is the opposite pattern: a long, narrow skull that looks boat-shaped from above. This one results from premature fusion of the suture running along the top of the skull, not from positioning. It’s the most common single-suture craniosynostosis.
Positional Flattening vs. Craniosynostosis
The critical distinction is between a flat head caused by external pressure (positional) and one caused by a skull suture fusing too early (craniosynostosis). Positional flattening is common and almost always harmless. Craniosynostosis is rare and requires medical evaluation.
A few clues help separate them. In positional plagiocephaly, the ear on the flat side shifts forward. In craniosynostosis of the lambdoid suture (at the back of the skull), the ear on the affected side is pulled downward and backward instead, and the head looks more like a trapezoid than a parallelogram from above. If a coronal suture (running from ear to ear) fuses early, the forehead flattens on that side and the eye socket on that side may appear drawn upward.
Run your fingers gently along the lines where the skull bones meet. If you feel a hard, raised ridge rather than a soft seam, that could indicate a fused suture. A single ridge along the center of the forehead (the metopic ridge) is actually common and on its own does not mean anything is wrong, as long as the forehead has normal volume and the eyes aren’t unusually close together.
How Severity Is Measured
Doctors measure asymmetry using a simple metric: they compare the two diagonal distances across the skull. The difference between the longer and shorter diagonal, expressed as a percentage, gives a severity score. A difference under 3.5% is considered normal. Between 3.5% and 6% is mild, 6% to 10% is moderate, and above 10% is severe.
You can approximate this at home with a flexible measuring tape, though clinical measurements taken with calipers or a 3D scanner are more precise. If the asymmetry is visible but subtle, it’s likely in the mild range. If the ear shift and facial unevenness are obvious to family members who see your baby regularly, it may be moderate or beyond.
Checking an Older Child or Adult
Adults and older children who had a flat head in infancy sometimes still carry a degree of asymmetry. The signs are the same: one side of the back of the head flatter than the other, ears not perfectly aligned, or subtle differences in facial fullness from left to right. Many adults discover it when a hairstylist mentions it, when a hat sits unevenly, or when they feel the back of their own skull and notice one side doesn’t match the other.
In adults, positional flattening from infancy is purely cosmetic. The skull bones have fully hardened and the shape is permanent, but it doesn’t cause headaches, cognitive issues, or other health problems.
When the Shape Matters Most
For babies, timing is everything. The skull is most malleable in the first several months of life, which means both that flat spots develop quickly and that they can improve quickly with intervention. Simple repositioning, like alternating which direction your baby faces during sleep and increasing supervised tummy time, works well for mild cases.
If repositioning hasn’t improved the shape by around four months, or if the asymmetry is moderate to severe, a cranial molding helmet is the standard treatment. Helmets are most effective when started before eight months of age, while the skull is still growing rapidly. After about 12 to 14 months, the bones become rigid enough that a helmet offers little benefit.
If you notice a raised ridge along any suture line, the head shape worsening rather than improving, or the asymmetry involves the eye socket being drawn upward, those warrant a medical evaluation to rule out craniosynostosis. Craniosynostosis typically requires surgical correction, and earlier diagnosis leads to better outcomes.