While graying hair is one of the earliest and most noticeable signs of aging, few people outside the health and beauty industries actually understand what causes gray hair. To understand gray hair, you must first understand what causes hair color.
The tube-shaped opening in the skin that leads from the root of a hair to the surface of the skin is called a follicle. At the base of the follicle, keratinocytes, or epidermal cells, form the structure of the hair. These epidermal cells eventually die, leaving mainly keratine, which is colorless. While this is going on, melanocytes deliver packages of melanin, called melanosomes, to the keratinocyces. It is these packages of melanin that give hair its color. Melanosomes come in two basic colors, eumelanin (dark brown or black) and pheomelanin (yellow or red). Different combinations and ratios of these two basic color blocks provide the wide variety of hair shades we see in nature.
The Follicle Life Cycle
Humans have thousands of follicles on their heads, and at any given moment approximately 80 to 90 percent of them are in an active cycle. Active cycles last for approximately two to seven years, and then the follicle dies, which results in the hair falling out. After death, the follicle must rebuild itself from the stem cells that form both keratinocytes and melanocytes. For reasons that aren’t well understood, keratinocytes are hardier than melanocytes and survive more follicle death and rebirth cycles, resulting in follicles still capable of building and growing hair, but with less and less ability to supply the hair with melanin as time goes on. Hair begins to fade to gray and then eventually turns white, which indicates the total absence of melanin in the hair shaft.
Genetics Play a Role
Everything else being equal, you should begin to go gray about the same time your parents and grandparents did. Men tend to begin graying around age 30 while the average for women is closer to 35. The first gray hairs usually appear around the temples. While those with lighter hair generally look less gray for longer, because gray hair is camouflaged by the light hair around it, those with darker hair actually gray more slowly. Graying occurs earliest in Caucasians and latest in Asians. Body hair tends to go gray more slowly than the hair on your head, and may never gray completely.