The Effects of Aging on Hair–More Than Just Amount 462 to peak in the forties, but for 46 women, ages 38–68, who displayed hair loss, the peak was in the fifties. The study by Nagase et al. on 132 Japanese females, ages 10–70, shows the minor axis diameter of hair fibers taken from the “top of the head” to peak near age 40. Trotter and Dawson conducted two studies on hair fiber diameter versus age.19, 20 One study19 on hair taken from the vertex of 132 French-Canadian females, ages 0–89, shows an increase in mean fiber diameter in those in their teens through to those in their late 30s (from a quadratic model of their data on hair diameters) and a decrease thereafter. The second study20 was on hairs taken from the vertex of 211 American females. These females showed an increase in fiber diameter from childhood up through the early 40s (from a quadratic model of their data on linear densities). A study by Jackson, Church and Ebling21 used the same data in a publication by Ebling.22 Hair fiber diameter was measured on 20 hairs plucked from the vertex from 125 female Caucasians, Figure 1.