Hair

Melanin is the brown pigment produced by cells termed melanocytes. These cells lie in the bottom layer of the epidermis. The amount of dark pigment that is produced declines with age. At the same time, the central medullary space of the shaft enlarges. Light reflection from the cell surfaces of the cuticle and cortex is also increased. The combination of these changes is generally accepted as the cause of hair graying with age. It is more obvious in dark-haired individuals but appears more complete in lighter haired individuals. The whole process is under genetic control.

There are racial variations. While graying appears as early as twenty years of age in Caucasians Figure 1 Hair Bulb and Follicle: The Cycle of Hair Growth SOURCE: Based on Montagna, W. The Structure and Function of Skin, 2nd ed. New York: Academic Press, 1962. and at thirty in Africans, the first appearance of gray hair generally occurs at around thirty-five in Caucasians. By age fifty, 50 percent of the population has some degree of significant graying. The process starts about five years later in Africans, and five years earlier in Japanese. Beard and moustache hair changes before the scalp and body hair. On the scalp, the temple hair grays first, followed by the crown and then back of the scalp. The whole process is a normal physiological change. In any given individual, the age at which graying becomes noticed, and the rate of graying, is not related to the overall rate of biological aging.