When will your baby's hair grow in?

Some babies are born with a full head of hair, while others have only a sparse covering. Mostly, it comes down to genetics: Just as the genes passed on from the parents affect a baby's eye color, they also affect how much hair is present at birth (and what color that hair is!).

Another thing that may play a role in newborn hair? Hormones. The old adage about mothers with a lot of pregnancy heartburn having babies with more hair may actually be partly true – a small studyOpens a new window has found that the same pregnancy hormones that cause heartburn may be responsible for fetal hair growth.

However much hair your baby has at birth, you might be wondering when it'll start filling in more. It's hard to say; infant hair growth patterns vary widely. Here's what to know.

When will your baby's hair grow?

Your baby's hair will usually grow in between the ages of 6 and 12 months, though all babies go through this stage of development in their own time.

But before that, all babies develop a layer of fine hair, called lanugo, in the womb. It can cover many parts of their body, including their head, face, back, and shoulders.

Many babies lose most or all of this lanugo before birth, but some will be born with it. It usually falls out a few weeks after birth.

As for the hair on your baby's head, that's a different story. Babies start growing hair follicles around 14 weeks gestation and are born with all the hair follicles they'll ever have. But that doesn't mean hair will actually be growing out of those follicles from the get-go; some babies are born with little to no hair, while others arrive sporting a full head of thick locks.

Whatever hair your baby has at birth is likely to fall out in the first few months, anyway. This baby hair isn't meant to be permanent, and shedding it makes way for more mature hair to grow in.

Is baby hair loss normal?

Usually, yes. Hair loss in babies typically peaks when they're around 3 months old; not coincidentally, this is often when new moms start shedding hair postpartum too. Most likely, it's the decrease in hormones after birth that triggers hair loss in both moms and babies.

It's also common for babies to lose a patch of hair on the back of their head from all those hours sleeping on their back or hanging out in infant seats (the same reason babies sometimes develop what's called flat head syndrome). This is called friction or pressure alopecia, and usually resolves once your baby begins sitting up unassisted, since they're spending less time lying on their back.

Sometimes babies' hair grows right back in, but in a different color or texture. In other babies, it takes a while to grow back.

Either way, your child will have normal hair growth at some point, though it may take time to be noticeable. If your baby's hair doesn't start growing by the time they're a year old (or six months after they began sitting up), let your child's pediatrician know.

Learn more:

• Is it normal for your toddler to have body hair?
• How to care for your Black baby's hair