The Effects of Aging on Hair–More Than Just Amount 464 parietal sites on more than 1,000 female Caucasians, ages 18–66. In addition, they measured hair densities on analogous sites on these same women. They concluded that hair diameter in the parietal region increases until approximately 45 years of age and decreases with increasing age thereafter. The age for maximum diameter is clearly higher than for maximum density, and menopause with its physiological changes, including estrogen changes, plays a more important role in hair diameter. On the other hand, the study by Otsuka and Nemoto15 indicated maximum hair diameter at around age 40. Since this study was done on more than 18,000 Japanese females, ages 10–60, it has to be considered relevant despite the fact that no additional experimental details were provided in that paper. If the menopause and its consequent physiologic changes are involved in the age for maximum diameter and subsequent changes, we would expect the peak to be closer to age 45 than age 40. But the difference between these two studies might also be explained by a geo-racial or population effect. Additional studies will be required to resolve this issue, however, since the median age for menopause occurs at approximately age 50 in women of most industrialized countries, including Japan and the United States,17 we lean toward the effects of menopause being critically involved and therefore suggest that the age range for maximum diameter for both populations is likely to be closer to the mid-forties. Puberty through adulthood for men: For Japanese males, the study by Otsuka and Nemoto shows that scalp hair fiber diameter increases to a maximum in the late teenage years and then decreases relatively rapidly with increasing age. This study suggests a larger effect of age on hair fiber diameter for men than for women (Table 4). The study by Trotter and Dawson on only 82 male French Canadians shows a similar effect qualitatively: a peak in diameter in the late teens for men and a decline after that.19 The work of Courtois et al.25 on the same 10 French male subjects over a period of several years provides support for a decrease in hair diameter of male Caucasians ranging in age from the mid