Why Do Babies' Eyes Change Color?

In this episode of mental_floss' Big Questions, Craig answers a question from one of our YouTube fans: "Why do babies' eyes change color?"

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Hi I'm Craig, my eyes might be brown, but my heart burns red for you, and this is mental_floss video. Today I'm gonna answer YouTuber doxysrkx's Big Question, "Why are babies born with blue eyes?" It's true that the majority of Caucasian newborns have blue eyes, but by adulthood only one in five have them. That's because eye color can change for white babies. African, Hispanic, and Asian babies are typically born with brown eyes which don't change color. Let's get started.

First, let's talk about what eye color is. Whether your eyes are brown, green, hazel, or blue has to do with something called melanin. It's basically a type of pigment which can also affect the colors of your skin and hair.

Your eyes contain melanocytes, which are cells that produce melanin. If there's a lot of melanin, the eyes are brown, if there's a medium amount, they're green or hazel, and a little bit means blue eyes. Another thing that affects eye color is the Tyndall effect, which is virtually identical to Rayleigh scattering, a concept you remember from our episode on whether blood is blue. I don't remember 'cause we do a million of these videos. And I'm usually drunk. But that explains why eyes may look different colors in different light; it doesn't affect whether eyes actually change color.

Newborns don't have the levels of melanin that they'll eventually have; the amount increases over time, which is why eyes often start blue then change to another color. They go from a small amount of melanin, which you'll remember causes eyes to be blue, to a larger amount which means they'll be a different color. Usually this happens around six months, but eyes can change color up to about three years old. And the reason this only happens for Caucasian babies is because they tend to be born with less pigment than other ethnicities.

So does this mean that your biology teacher was lying to you and eye color is more about melanin than genetics? Well no, it is genetic, they might've been lying to you about something else—I don't know, I don't know your biology teacher. But we now know that the genetics associated with eye color are more complicated than we once thought. You can't map it out on a simple chart because there are a handful of genetics that come together to affect eye color. In fact, experts predict that there are about 15 of them, and melanin production is just a little piece of the puzzle.

Supposedly, there's a way to tell whether or not eye color will change by looking at a baby's eye from the side so that there's no light affecting your view. If there are hints of gold in the iris, you're rich! No, the eyes will probably become brown or green over time. If the eyes are still very blue, they'll probably stay that way. This needs to be properly studied though. And I'm not gonna do it. Someone will eventually.

Thanks for watching mental_floss video, which is made with the help of all of these cute widdle babies. If you have a big question of your own that you'd like answered, leave it below in the comments. I'll see you next week, with these brown eyes.