The Effects of Aging on Hair–More Than Just Amount 480 curvature, fiber length, color (hair and scalp) and style, and relates very much to hair body or the amount of hair. And since Mirmirami and Dawson have shown scalp site effects on diameter and density, scalp site will also have to be considered for a more complete model. The impact of hair color on the perception of graying and relative scalp coverage: The occurrence or incidence of any gray (look back to Table 1’s data from Keogh and Walsh6) are higher in the darkest hair and lowest in the lightest colored hair. Keogh and Walsh pointed out that lighter gray hairs can be observed more readily against a dark hair background than light hairs against a light hair background. But this effect is reversed for the incidence of completely gray hair which is perceived to occur earlier for the lightest hair color and last for the darkest hair. This effect of hair color relative to its background is why Robbins et al.16 suggested a related effect in the perception of relative scalp coverage which should be studied and determined. Trotter and Dawson19 determined that the hair of children tends to be lighter in color than adult hair as observed in 310 French Canadians, and summarized in Table 11. In this study, for adults, if any gray hairs were present they were removed and only pigmented hairs were included in the comparisons. Trotter and Dawson20 also examined hair of 340 American Caucasians in a similar manner and arrived at the same conclusion regarding age and hair color. Therefore, for these two Caucasian groupings it would appear that from childhood through the early teenage years hair tends to become darker and then sometime in the twenties and beyond, as hair becomes grayer, the overall color of Caucasian hair becomes lighter. For relative scalp coverage, as the color of hair changes relative to the scalp, the perception of scalp coverage will change, and determination of the quantitative relationship of this variable to relative scalp coverage remains an area for future investigation.