A flat spot on the head is almost always the result of sustained pressure on one area of the skull during infancy, when the bones were still soft and malleable. This condition, called positional plagiocephaly, affects up to 20% of all babies and as many as 40% in some populations. If you’re an adult noticing your head shape now, the flattening likely happened in the first few months of life and simply became your permanent skull shape once the bones hardened. If you’re a parent noticing it on your baby, the good news is that it’s a cosmetic issue with no effect on brain development, and it’s often correctable.
How Infant Skulls Get Flat Spots
A newborn’s skull is made of separate bones connected by flexible seams called sutures. This design allows the head to pass through the birth canal and gives the brain room to grow rapidly in the first year of life. The trade-off is that these soft bones reshape easily under pressure. When a baby’s head rests in the same position for long stretches, the skull flattens in that spot.
Back sleeping is the most common trigger. Since pediatricians began recommending back sleeping to reduce the risk of sudden infant death syndrome in the 1990s, rates of positional flattening have increased significantly. Car seats, bouncers, swings, and any surface where a baby’s head rests against a firm backing can contribute when used for extended periods.
Some babies are born with flattening already present. A cramped uterus, especially with twins or multiples, can press on the skull before birth. Births involving forceps or vacuum extraction also increase the risk. First-born children and males are slightly more likely to develop flat spots.
The Role of Neck Muscle Tightness
A surprisingly common contributor is a condition called congenital muscular torticollis, where one neck muscle is shortened or tight from birth. This pulls the baby’s head into a tilted position, with the chin pointing toward one shoulder and the head leaning toward the other. Because the baby can’t easily turn their head, the same spot on the skull absorbs pressure during every nap and overnight sleep.
Torticollis and flat spots often appear together. A physical therapist can teach parents stretches and positioning techniques to loosen the tight muscle and encourage the baby to turn toward their less-preferred side. Addressing the neck tightness early is one of the most effective ways to prevent the flattening from getting worse.
Positional Flattening vs. Craniosynostosis
In rare cases, an unusual head shape isn’t caused by external pressure but by a condition called craniosynostosis, where one or more of the skull’s flexible seams fuse too early. This restricts how the skull can grow and forces it into an abnormal shape. Unlike positional flattening, craniosynostosis is present at birth and can sometimes lead to increased pressure inside the skull, potentially affecting brain development.
The two conditions look different on examination. Positional flattening creates a flat area on the back or side of the head, and the skull feels smooth. Craniosynostosis produces a more rigid, sometimes ridged area along the fused seam, and the head shape changes tend to be more pronounced and asymmetric in specific ways. A pediatrician can usually distinguish between the two during a physical exam, though imaging is sometimes used to confirm.
How Severity Is Measured
Doctors assess the degree of flattening by measuring the difference in diagonal dimensions across the skull. A difference of less than 5 millimeters is considered normal. Mild flattening falls in the 5 to 10 millimeter range, moderate is 10 to 15 millimeters, and anything above 15 millimeters is classified as severe. These measurements help determine whether repositioning alone will be enough or whether helmet therapy might be recommended.
Correcting a Flat Head in Infancy
For mild cases, simple changes in positioning are often all that’s needed. The American Physical Therapy Association recommends a minimum of 5 to 10 minutes of supervised tummy time at least five times per day, gradually building up to 30 to 60 minutes total. Tummy time takes pressure off the back of the skull and strengthens the neck and shoulder muscles that help babies control their head position.
Beyond tummy time, there are several practical steps that make a real difference:
- Alternate crib orientation. Switch which end of the crib you place your baby’s head. Babies tend to turn toward light, sound, or a parent’s voice, so changing the direction encourages them to rest on their non-flattened side.
- Limit time in containers. Car seats, bouncers, swings, and infant seats should be limited to no more than one or two uses per day, each lasting 15 minutes or less. Car seats are for travel only.
- Carry your baby more. Holding your baby in your arms or using a wearable carrier keeps pressure off the flat spot entirely.
- Reposition during awake time. Whenever your baby is awake, position them to avoid pressure on the flat area.
When repositioning and physical therapy aren’t enough, or when flattening is moderate to severe, a cranial remolding helmet may be recommended. These custom-fitted helmets work by leaving space where the skull needs to grow while gently redirecting expansion away from the already-prominent areas. Babies who start helmet therapy younger tend to wear the helmet for less time and see better results. Starting before 8 months is ideal, though babies referred later can still benefit with a longer treatment period. The helmet works by harnessing the brain’s rapid growth during the first year of life.
Why Adults Still Have Flat Heads
If you’re an adult wondering about your own flat head, your skull shape was almost certainly set during infancy and became permanent as the bones fused. The major skull sutures close at different ages. One seam along the forehead fuses as early as 3 to 9 months. The seam running along the top of the skull typically closes around age 22, and the one across the back closes around 26. Once these seams fuse, the skull no longer reshapes in response to pressure.
For most adults, a flat head is purely cosmetic and causes no health problems. There is no exercise, pillow, or lifestyle change that will reshape an adult skull. If the shape causes significant distress, a surgical procedure called cranioplasty can reshape or contour the skull. This is a major surgery performed in close proximity to the brain, and it carries real risks including infection, blood clots, seizures, and stroke. It’s typically reserved for noticeable deformities or defects rather than mild cosmetic concerns.
Many people go their entire lives without realizing their head is slightly flat until they try a short haircut or feel the back of their skull closely. Some degree of asymmetry is normal in every human skull. If your flat spot doesn’t cause pain, headaches, or any functional issues, it’s simply a feature of your anatomy shaped during the first few months of your life.