Each hair on your head consists of two parts: a root and a shaft. The root keeps the hairs on your head by anchoring them to your scalp. The shaft is the “long" colored part of hair you see growing on your head. Each root of hair is nested in a tube-like follicle. Follicles contain special kinds of pigment cells that produce a chemical called melanin.
If you have ever had a suntan, you've already experienced melanin in action. One of its important jobs is to help absorb harmful ultraviolet radiation from the sun and protect your cells from damage. Though melanin does a great job, it isn't perfect, which is why it is important to always wear sunscreen when you head outdoors.
When it comes to hair, whether you're a blonde, brunette, or a redhead (or somewhere in between!), you can thank melanin. As a person ages, the pigment cells in the hair follicles begin to die. Much like a suntan begins to fade after a few days, when there are fewer pigment cells in the hair follicle, hair color begins to fade too.
In many older adults, this fading gives the hair a transparent color, appearing silver, white, or gray to the human eye. Though gray hairs are most noticeable in those with dark hair due to the contrast, people with lighter hair are equally likely to go gray.
What does this mean for a youngster? There is no way to know exactly when you will discover your first gray hair. What we do know is that going gray is influenced by genetics. This means you can roughly estimate based on the age your parents and grandparents were when their hair first started to change.