The Effects of Aging on Hair–More Than Just Amount 452 the relative contributions of these changes in hair with age on overall hair assembly properties and consumer perception however, we propose that diameter changes with age are likely to impart a large impact on overall perception of hair aging (described in detail in text). The hope is that a better understanding of how hair changes with age will enable the design of new cosmetic treatments that combat or reverse these effects. Fiber Properties—Part I: Color Graying of hair with age: For scalp hair, graying (canities) generally begins in the temple region and it spreads to the vertex or crown and finally to the remainder of the scalp, usually affecting the occipital region last. Graying is an expression of a gradual decrease in the function of the melanocytes,1 the pigment producing cells located near each hair bulb in the lower region of the follicle. A relatively small number of melanocytes can produce an intensely pigmented hair fiber of 1 meter or longer. These melanocytes function in 7 to 15 different hair cycles to produce pigmented hairs for up to four decades or longer.2 Each group of melanocytes in each follicle functions independently of similar groupings in neighboring hairs. Graying results from a decrease and the eventual termination of the activity of the enzyme tyrosinase in the lower bulb.3 This enzyme is involved in the reaction called Raper’s scheme for the formation of 5,6-dihydroxyphenylalanine, which is transformed into its corresponding quinone starting with the amino acid tyrosine.4 Subsequently, this species reacts further to produce the hair pigments. Kukita3 has shown that the onset of tyrosinase activity coincides with the appearance of melanocytes during anagen and its activity increases rapidly with increasing numbers of melanocytes. Tobin et al.5 have summarized the regulation of coat color in hairy mammals by POMC-derived peptides (α-melanocyte stimulating hormone, adrenocorticotropic hormone, and β-endorphin). The expression of these peptides and the melanocyte-1 receptor (MC-1R) are confined to specific regions of the hair follicle and are adjusted or controlled