What causes gray hair?

Hair gets its color from the pigment melanin, the same agent that colors skin and eyes. The color is contained in the hair shaft, which is composed of long, tapering cells that have coalesced into fibrous material. Color is inherited, along with the degree and timing of graying. Gray hair is not really gray but an absence of color in the hair shaft, rendering it white or opaque. Graying usually starts (or you could say that natural pigmentation usually stops) at the hairline and progresses toward the back of the head. The “gray,” unpigmented hairs tend to be coarser than the colored hairs.