492 JOURNAL OF COSMETIC SCIENCE Diameter vs Young's Modulus 2 0 ,.......! X 1.5 • 0 40 50 60 70 80 90 Diameter ( µ m) Figure 8. Relationship between diameter and Young's modulus (3). Japanese females (age: 26--39, N = 21) and Caucasian females (age: 20--40, N == 35): ♦. Japanese females (age: 45-51, N = 17): lighter•· Japanese females (age: 45-51, N = 9) with hair trouble such as less hair volume: darker e. Degradation of Young's modulus with aging is induced by not only a decrease in hair diameter bur also by intrinsic structural changes. shown in Figure 4, the Japanese hair was more round than the Caucasian, and so the cross-sectional area moment may be smaller to make the apparent Young's modulus bigger. Interestingly, the data of Japanese panelists' hair over 40 years old fluctuates (Figure 7: the symbol e is used for panelists over 40 years old). In order to explain this phenom­ enon, the data of the panelists' consciousness about hair was analyzed. In this data, the biggest concern of senior female panelists was hair graying and the next was a decrease in volume and bounce. The Young's modulus of hair from those who suffer from a decrease in volume and bounce is shown using the darker symbol • in Figure 8. These black symbols are located beneath the others, and the mean Young's modulus of this group is ca. 10-30% lower (Table I). This result indicates that the decrease in volume and bounce with aging is caused not only by a decrease in hair thickness and a decrease in the number of hair fibers per square centimeter of scalp but also by a decrease in the Young's modulus, which must be caused by some internal change in the hair fiber, such

DECREASE IN HAIR VOLUME WITH AGE Japanese females (age: 26-39, N = 21) and Caucasian females (Age: 20-40, N = 35 Japanese females (age: 45-51, N = 17) Japanese females (age: 45-51, N = 9) with hair trouble such as less hair volume Table I Results of Analysis by ANOV A Japanese females (age: 26-39, N = 21) and Caucasian females (age: 20--40, N = 35) 0.33 0.00015 Japanese females (age: 45-51, N = 17) 0.091 493 Japanese females (age: 45-51, N = 9) with hair trouble such as less hair volume Each figure means the significance probability. Japanese females with hair trouble such as less hair volume show significant differences from other Japanese females (age: 26-39) and Caucasian females (age: 20--40). as a change in structure or components. A few reports have referred to the relationship between age and hair shaft properties, such as hair diameter and tensile strength (13- 17, 18). Kususe (18) has reported the same tendency as with these results by using tensile testing, that is, the Young's modulus decreases with aging. Regarding the internal change in hair with aging, changes in the lipid components have been reported (19). It was also reported that the ratio of the lipid originating from the sebum cutaneum increases with aging (20). These internal lipid changes may be the cause of the difference in the Young's modulus. However, further and wider study will be needed to clarify what are the main causes of this difference, because some funda­ mental changes in the internal structure and/or components of the hair must occur with aging. CONCLUSIONS One of the biggest concerns for the aged female, regardless of nationality, is the decrease in volume and bounce. The bending stress is thought to be a good physical parameter to represent hair volume and bounce however, it has not been easy to measure it in a reproducible manner. In this study, a new methodology, in which a small mass of hair fibers from the chemically untreated part of hair (within a few centimeters from the scalp) could be measured at once, was developed. By using the data of bending stress obtained by the new methodology, Young's modulus, which is not dependent on the cross-sectional area of the hair fiber, was calculated. By comparing the resulting data of the fibers collected from the panelists younger than 40 years old, no significant difference in Young's modulus between Japanese and Caucasian hair was recognized, and the modulus was ca. 10 GPa, regardless of the hair diameter. On the other hand, there existed cases in which fibers showed lower Young's moduli, and these fibers were from senior panelists who were conscious of the decrease in hair