A flat spot on the back of a baby’s head can be startling in photos. In most babies it is linked to the way they lie, but a few causes need a doctor’s attention, so telling them apart matters.
Why It Happens
A baby’s skull is soft and its bones are not yet fused, so lying on the same spot for long stretches can flatten it. This is called positional plagiocephaly. The AAP’s 2020 clinical report, “Identifying the Misshapen Head,” stresses distinguishing it from craniosynostosis, in which skull bones close too early. The report says most cases can be identified from the history and an exam that looks at the head from the front, back, and top. In positional flattening the ear on the flat side is often pushed forward, which is a different pattern from lambdoid synostosis. AAP news materials describe positional plagiocephaly as an aesthetic condition, with no credible medical evidence that it affects brain development as long as babies sleep on their backs.
How It Differs by Age
Flattening often becomes noticeable in the first weeks to months, and it tends to improve as babies roll over, sit up, and spend less time on the flat side. Secondary summaries of the older 2011 AAP report say repositioning works best when started before about 5-6 months. That report was retired in 2018, so treat it as background rather than current advice, and ask your pediatrician about timing.
Care at Home
Keep placing the baby on the back to sleep. During awake, supervised time, offer tummy time several times a day, starting with a few minutes and building up. Holding or carrying the baby more often reduces time lying on the flat spot. In the crib, alternate which end the baby’s head points toward so pressure does not always fall on one side, and move mobiles or your own position to encourage looking the other way. If the baby strongly prefers turning the head to one side, ask about torticollis, a tight neck muscle. Avoid pillows, wedges, or positioners to reshape the head during sleep because they raise suffocation risk.
Common Misunderstandings
Many parents worry a flat head signals a brain problem, but AAP materials describe no credible evidence of that for positional flattening; some sources still suggest watching development, so keep well-child visits. Others assume a helmet is a must. Studies of helmets are mostly observational and results are mixed, and reviews have questioned helmets as a standard treatment for healthy infants with mild deformity. Some believe a firm pillow will round the head, which is dangerous and should be avoided. And tummy time never means tummy sleeping: sleep is always on the back.
When to Seek Medical Care
After any head bump, go to the emergency room right away if a baby keeps vomiting, is hard to wake or limp, or has a seizure. A bulging, tense soft spot with fussiness or fever also needs urgent care. Otherwise, see a pediatrician if you feel a ridge along the back of the skull, the forehead juts out on one side, head circumference is crossing growth-chart lines quickly, or the shape worsens instead of improving, so craniosynostosis can be ruled out. This information is based on U.S. (AAP) guidance; if you live elsewhere, check with a local pediatrician for country-specific recommendations. This information isn’t a diagnostic tool and doesn’t replace advice from a medical professional.