Why Do Babies Have Such Big Heads?

On Oct. 19, 42-year-old heiress Paris Hilton posted a photo of her son, Phoenix Barron, on Instagram, both of them smiling happily at the camera.

She wrote, “My precious angel baby Phoenix’s first time in NYC. ✨👱🏼‍♀️👶🏼🗽✨”

The comments quickly turned ruthless as people remarked on the size of the baby’s head and even speculated about possible medical diagnoses, prompting Hilton to respond with her own comment: “🥺😢There are some sick people in this world.☹️My angel is perfectly healthy. And yes, of course he has been to a doctor, he just has a large brain.”

Dr. Janine Zee-Cheng, a pediatrician who practices in Indiana, told HuffPost that they thought it was terrible that “people were picking on a literal baby.”

They also explained why babies’ heads tend to appear large, saying that when it comes to head size, there is a wide range of what is considered normal — and the only person who needs to know your child’s measurements is their doctor.

Why do some babies’ heads look big?

It’s true that some babies’ heads appear large. If you’re looking at photos, don’t forget that camera angle can play a role here, too. But babies are also simply built differently from adults.

“Babies’ heads are just proportionally bigger than adult heads with respect to the rest of their bodies. That’s just how we are when we are small — and that is a normal thing,” Zee-Cheng said.

Human brains evolved to be this way. We have the largest brain relative to our body size among all animals. Our brains are three times the size of those of our closest primate relative, the chimpanzee. Interestingly, our brain-to-body ratio is actually closest to that of rodents.

As far as variation among humans is concerned, Zee-Cheng noted that genetics play a decisive role: Parents with bigger heads tend to have babies with bigger heads. The clinical term for a large head is macrocephaly, and when it’s an inherited trait, it’s known as benign familial macrocephaly. Macrocephaly is diagnosed in 2-5% of the population, according to the Cleveland Clinic.

If you believe a baby’s head looks big, it’s likely the result of normal human variation.

Why do pediatricians always measure a baby’s head circumference?

There are, however, instances when head size (small or large) can indicate a problem that needs to be addressed. This is why pediatricians measure an infant’s head circumference at every check-up.

“If you look at the CDC growth charts for infants, you’ll see the head grows very quickly in the first few months of life,” Zee-Cheng said.

Dr. Jodi Smith, a pediatric neurosurgeon at Peyton Manning Children’s Hospital in Indianapolis, told HuffPost, “We know that a baby’s head should grow about a centimeter a week.”

Doctors monitor infants’ head growth by locating a child’s measurements within a growth percentile. For example, a child whose head circumference is in the 50th percentile has a bigger head than half the babies their age and a smaller head than the other half.

The percentile your child’s measurements fall into is less important than the rate of growth their doctor is seeing. If your child’s measurements jump (or drop) in percentiles, your doctor may refer you to a neurosurgeon, who will examine your child and may order imaging to rule out a medical issue.

“If the rate of growth is too quick, or if the rate of growth is too slow, then that can be associated with underlying concerning things,” Zee-Cheng said.

Smith said that for the babies who are referred to her, “the first and the easiest thing that we deal with” is known as benign extra-axial fluid of infancy, which simply means there’s “a little bit of extra fluid on the outside of the brain ... that causes the head to grow.” She noted that it’s “a benign condition [and] doesn’t need to be treated.” In these cases, the child’s head growth usually plateaus around the time they are 18 months old. Sometimes milestones like walking are delayed, which Smith attributes to a baby needing to hold up and balance a heavier head.

Unfortunately, large head size can also be caused by “accidental trauma, shaken baby syndrome or abuse,” she said. Such trauma can cause blood vessels to rupture. In these cases, it is blood from the internal injury, not an excess of cerebrospinal fluid, that causes the unexpected growth of the baby’s head.

Other less common findings include hydrocephalus, an excess of fluid on the brain. Every person produces cerebrospinal fluid every day. When “that fluid is blocked in any way, [it ends up] putting pressure on the brain, which puts pressure on the skull and causes the head to grow big,” Smith explained. The condition is usually treated by placing a shunt so that the fluid can drain. Tumors can also cause this kind of blockage.

Treatment for any of these conditions is facilitated by early diagnosis. “The earlier we find them — before the baby’s really having problems — that’s going to be the best situation,” Smith said.

Why do some babies wear helmets?

Because babies’ heads grow so quickly, the bones of their skull must be able to adjust. There is flexible material, called a suture, between the plates of a baby’s skull, and these bones don’t fully fuse together until a child is about 2 years of age.

Thus, if there are any issues with the way that a child’s skull is forming, they’re best addressed during these first years of a child’s life.

“As the baby grows, the plates and the skull will eventually fuse together, and then it becomes harder to correct things,” Zee-Cheng explained.

You may have seen an infant wearing a helmet. This treatment is meant to help a baby’s head grow correctly, although it is much less common than it used to be, Zee-Cheng noted.

Many babies develop a flat spot on the back of their heads as a result of always being laid to sleep on their backs (per safe sleep guidelines). The scientific name for this is positional plagiocephaly. In the past, babies with this condition were frequently given helmets, but doctors now know that the issue usually resolves on its own and doesn’t require treatment. Parents may be advised to have their babies spend more waking hours in supervised tummy time or being held by a caregiver, rather than lying on their backs, to help their heads grow evenly.

Other concerns about the shape of a baby’s head, such as an overly prominent forehead or asymmetry of the eyes, may still be treated with helmet therapy.

If the bones of a baby’s skull fuse together prematurely, this can also cause issues. Because the bones are fused, they cannot be corrected with helmet therapy and generally require surgical treatment. Again, early diagnosis is helpful.

Trust your instincts.

If you have concerns about the size, shape or growth of your baby’s head, talk with your pediatrician. It’s their job to answer your questions and to listen to you if you think a referral to a specialist is warranted.

“A mommy or daddy’s gut intuition is always the most important,” Smith said.