Why some people go gray in their 20s, according to a dermatologist

We asked a dermatologist to explain why hair turns gray, and why it can happen to some people as early as their 20s.
According to Dr. Jennifer Chwalek, genetics will likely determine whether or not you will go gray, and how soon it will happen.
Our hair pigment is protected by an enzyme that fights the build-up of hydrogen peroxide.
As we age, this enzyme declines, allowing the hydrogen peroxide to break down the melanin in the hair shaft, causing the color to change.
According to Chwalek, factors like stress and smoking that cause oxidative damage could also contribute to hair going gray.
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Following is a transcript of the video.

Graham Flanagan: Look at that silver fox. So distinguished, so sophisticated. Wow! But what if I told you that this guy was a millennial? It's true, just barely. According to Joe, he started going gray when he was 16. By 22, he was pretty much totally gray. Why does that happen? And why does hair turn gray in the first place? There's something about a silver fox, if you can pull it off.

Actor: When I got rid of my gray hair, I wanted a natural look. Graham: But many people hate the idea of going gray. There's an entire industry built around fighting it.

Actress: It's like you took off 10 years.

Actor: And in just five minutes.

Man: Just For Men. She'll love the way you look.

Flanagan: So why does it happen?

Dr. Jennifer Chwalek: The process of hair changing from darker color to white or gray with age is mainly due to genetics. It can be inherited from either parent. The color of our hair is determined by the form of hair pigment that we have. The pigment is actually produced along the hair shaft, and there are two main forms of hair pigment. There's eumelanin and pheomelanin. Eumelanin is what we see in brunettes and darker-haired people, and pheomelanin is what we see in blonds and redheads. The cells in our hair bulb produce a little bit of hydrogen peroxide, which is a metabolic byproduct, and typically there's an enzyme called catalase that breaks this down to water and oxygen. But as we age, there's declining levels of catalase, and this allows the build-up of hydrogen peroxide in the hair bulb, which damages and destroys the melanocytes, or the pigment-producing cells, of our hair.

Flanagan: So I wanted you to take a look at my colleague Joe here. Joe is technically a millennial. He started to go gray when he was 16, and by 22, it was pretty much gray all over. What happened to Joe?

Chwalek: So when individuals gray early in life before the age of 20, it's called premature graying, and this is due to genes. And we know there's one gene, in particular, that's been targeted called interferon regulatory factor 4, which is important in regulating and producing melanin in the hair. Joe was lucky enough to inherit some genes that predisposed him to developing gray hair early in life.

Flanagan: Obviously, Joe has gray hair on his head. When you go gray on your head, does the hair on the other parts of your body go gray as well? No, no, Joe, Joe! We can picture it.

Chwalek: So you can grow gray hair anywhere on your body. Wherever you have hair, the hair is susceptible to oxidative damage and eventually going gray.

Flanagan: So the main cause of going gray is genetics, but what role can stress play? After all, Obama didn't look like this when he showed up at the White House.

Chwalek: So it's controversial the role that stress has in hair graying. We know that stress creates oxidative damage in the body, and it's been linked to a lot of premature-aging syndromes. So it's thought that the stress, that stress causes oxidative damage, which may cause damage to the melanocytes and may cause us to grow gray earlier. We know that smokers tend to go gray more so than the general population, and again it's felt that it's probably due to the oxidative damage that smoke causes and how it affects the pigment-producing cells in the hair. I think eating a well-balanced diet, so you make sure that you don't develop any nutritional deficiencies, that's another thing that can be done. And modulating your stress. That's another thing you have control over, which over time can cause oxidative damage and, again, make you prone to potentially more gray hair.