Since the "Back to Sleep" campaign dramatically reduced SIDS rates, there's been a predictable trade-off: more babies develop flat spots on the backs or sides of their heads. This condition—called positional plagiocephaly—is very common, usually cosmetic, and almost always improvable with simple measures.
What Causes Flat Spots?
Baby skulls are soft and malleable by design—they need to be flexible to pass through the birth canal and to accommodate the rapidly growing brain. This same flexibility means the skull conforms to whatever surface it rests against most.
Common causes:
Back sleeping. The most common cause. Safe sleep is non-negotiable, but it does mean the back of baby's head gets a lot of pressure.
Position preference. Many babies prefer turning their head to one side. This creates asymmetric flattening on the preferred side.
Torticollis. A tight neck muscle that causes the head to tilt to one side and rotate to the other. This limits baby's ability to vary their head position, leading to uneven flattening.
Limited tummy time. Babies who spend most of their awake time on their backs (in swings, bouncers, car seats) get additional pressure on the same area.
Multiple births. Twins and multiples have cramped in-utero positions that can cause molding before birth.
Premature birth. Preemie skulls are even softer, and NICU babies often spend extended time in one position.
Types of Flat Head
Plagiocephaly: Flattening on one side of the back of the head. When viewed from above, the head looks like a parallelogram—one side is pushed forward relative to the other. The ear on the flat side may appear pushed forward.
Brachycephaly: Symmetrical flattening of the entire back of the head. When viewed from the side, the back of the head looks flat and the head appears wide.
Both are positional (caused by external pressure) and should be distinguished from craniosynostosis (premature fusion of skull bones), which is a different condition requiring different treatment.
When to Start Watching
Flat spots typically become noticeable around 6–8 weeks, when the birth molding has resolved and positional flattening has had time to develop. I check head shape at every well-baby visit.
What You Can Do
Tummy Time (The Most Important Intervention)
Every minute baby spends on their tummy is a minute of pressure off the back of their head. Aim for:
- Multiple short sessions throughout the day
- Goal: 30–60 minutes total by 2 months
- Include tummy time on your chest—it counts
Reposition During Sleep
While baby must sleep on their back, you can alternate which end of the crib their head is at. Babies tend to turn toward the room (toward light, sounds, activity), so switching ends changes which side of their head rests on the mattress.
Vary Holding and Carrying Positions
- Alternate which arm you carry baby in
- Use upright holds (head pressure on your shoulder instead of back of skull)
- Try the football carry (face down along your forearm)
- Babywearing in a carrier keeps baby upright with no back-of-head pressure
Limit Time in "Containers"
Car seats, bouncers, swings, and rockers all put pressure on the same spot. Use them for their intended purpose (safe transportation, brief settling) but don't let baby spend hours in them.
Address Position Preference
If baby always turns to one side:
- Place interesting things on the other side (your face, toys, a window)
- Alternate which side you approach for diaper changes and feeding
- Position the crib so baby has to turn the other way to see the room
- If the preference is strong and persistent, ask about torticollis
When Is a Flat Spot Concerning?
Most flat spots are mild and improve with repositioning alone. See your pediatrician if:
- The flat spot is severe or rapidly worsening
- There's a prominent ridge along a skull suture (could indicate craniosynostosis)
- Baby has limited neck mobility (possible torticollis needing physical therapy)
- The forehead or face appears asymmetric when viewed from above
- No improvement after 2–3 months of consistent repositioning
Helmet Therapy
Cranial remolding helmets are sometimes recommended for moderate to severe plagiocephaly or brachycephaly that hasn't responded to repositioning.
How they work: The helmet has space where you want the skull to grow and is snug where you don't. Baby wears it 23 hours per day for 2–6 months.
Best window: 4–6 months of age, when the skull is still very malleable. After 12 months, helmet effectiveness decreases significantly.
The evidence: Studies show that most mild to moderate cases resolve on their own by age 2, with or without a helmet. Helmets can speed up improvement and are most beneficial for severe or asymmetric cases. Your pediatrician can help you weigh the costs, benefits, and timing.
Cost: Helmets are expensive ($2,000–$4,000) and may not be fully covered by insurance. This is a factor in the decision.
Craniosynostosis: The Red Flag
Craniosynostosis is a very different condition where one or more skull sutures fuse prematurely. This restricts growth along the fused suture and can cause abnormal head shapes.
Signs that suggest craniosynostosis rather than positional flattening:
- A hard, raised ridge along a suture line
- Head shape that doesn't improve with repositioning
- Unusual head shape present at birth that worsens
- Very small or absent soft spots (fontanelles)
Craniosynostosis requires evaluation by a craniofacial specialist and sometimes surgical correction. It's much less common than positional plagiocephaly.
The Long View
Here's what I tell worried parents: the vast majority of positional flat spots improve significantly by 12–24 months as baby spends less time on their back, their skull hardens, and hair grows in. By age 2–3, most cases are barely noticeable.
Consistent tummy time, varied positioning, and addressing any torticollis are usually enough. Trust the process, keep up the repositioning, and know that this is a very common and very manageable part of modern baby care.