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Have you ever watched someone try to cover up gray hair by dyeing it? Or maybe you wonder why your granddad has a full head of silver hair when in old pictures it's dark brown. Getting gray, silver, or white hair is a natural part of growing older, and here's why.

Each hair on our heads is made up of two parts:

a shaft — the colored part we see growing out of our heads a root — the bottom part, which keeps the hair anchored under the scalp

The root of every strand of hair is surrounded by a tube of tissue under the skin that is called the hair follicle (say: FAHL-ih-kul). Each hair follicle contains a certain number of pigment cells. These pigment cells constantly make a chemical called melanin (say: MEL-uh-nin) that gives the growing shaft of hair its color of brown, blonde, black, red, and anything in between.

Melanin is the same stuff that makes our skin's color fair or darker. It also helps determine whether a person will burn or tan in the sun. The dark or light color of someone's hair depends on how much melanin each hair has.

As we get older, the pigment cells in our hair follicles gradually die. When there are fewer pigment cells in a hair follicle, that strand of hair will no longer contain as much melanin and will become a more transparent color — like gray, silver, or white — as it grows. As people continue to get older, fewer pigment cells will be around to produce melanin. Eventually, the hair will look completely gray.

People can get gray hair at any age. Some people go gray at a young age — as early as when they are in high school or college — whereas others may be in their 30s or 40s before they see that first gray hair. How early we get gray hair is determined by our genes. This means that most of us will start having gray hairs around the same age that our parents or grandparents first did.

Gray hair is more noticeable in people with darker hair because it stands out, but people with naturally lighter hair are just as likely to go gray. From the time a person notices a few gray hairs, it may take more than 10 years for all of that person's hair to turn gray.

Some people think that a big shock or trauma can turn a person's hair white or gray overnight, but scientists don't really believe that this happens. Just in case, try not to freak out your parents too much. You don't want to be blamed for any of their gray hairs!