Each hair on our heads is made up of two parts:
- shaft: the colored part we see growing out of our heads
- 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 which contains a number of pigment cells. These pigment cells continuously produce a chemical called melanin which gives the growing shaft of hair its color of brown, blonde, red, and anything in between.
Hair turns gray as people age because the follicles at the base of the hair shaft cease to produce melanin. The darkness or lightness of the hair depends on how much melanin each strand contains. Genetics is the most common cause of gray hair, but other things can contribute to graying, including a poor nutrition.