324 E u ....... en ::::J ■- -c f! "t: ::::J u 8 6 4 C 2- ftS :E 0 JOURNAL OF COSMETIC SCIENCE *** *** ·············································-----� * *** , ...................................---------. Frizzy I *** ... .. I Wavy Slightly wavy I Evaluated hair style l . Straight Figure 4. Relationship between the mean curl radius and the evaluated hair style. The hair style of 230 volunteers was evaluated and categorized into four types (see Experimental section). The mean curl radius of each volunteer was calculated from the curl radii of ten hair fibers and then the mean curl radius of each hair style was obtained. The error bar of each column indicates the standard deviation of that data set. Asterisk symbols indicate p-values obtained from Student's t-test: *p 0. 05, ***p 0. 001. only by the curl radius. The synchronicity of the curl phase of neighboring individual fibers is probably an important factor for forming a frizzy hair style. In the case of "frizzy" hair, the curl phase is not synchronized, while the curl phase is synchronized in "wavy" hair. MEASUREMENTS OF HAIR DIAMETER AND ELLIPTICITY The diameters of 8926 hair fibers from the randomly selected 132 Japanese women were measured. The distributions of the major and the minor axes of hair diameter are shown in Figure 5. The major and minor axes are distributed in the ranges from 30 to 1 70 µm and from 30 to 130 µm, respectively. The average major and minor axes are 95.3 ± 16.5 µm and 74.4 ± 10.5 µm, respectively. The ellipticity of hair was also determined from the ratio of major axis to minor axis. The distributions of the ellipticity are shown in Figure 6. The ellipticity is distributed in the range from 1.02 to 2.19. The average ellipticity is 1.28 ± 0.15. The average value of ellipticity is consistent with the reported values of Mongolian hairs and is lower than those values quoted for Ethiopian and Caucasian hairs (1). In the literature (1), it is discussed that hair curvature correlates with ellipticity among Caucasians, Mongolians, and Ethiopians. Interestingly, more curved hair shows a more elliptical cross-sectional shape among the above-mentioned human groups. We therefore investigated whether or not the same tendency was observed only within Japanese hair samples. Figure 7 shows the plot of the curl radius against the ellipticity of the hair

40 � 0 30 ..._ � u C 20 G) ::s D"' G) ... 10 LL 0 0 HAIR CURVATURE IN JAPANESE WOMEN N = 8926 fibers (from 132 volunteers) I I I I 50 0 ,, I \ I \ I I I I I 0 I I I I I I I I I I I 0 I \ \ q I \ \ \ 100 ------ Major axis --0-- Minor axis 150 200 Hair diameter/ 1,1m 325 Figure 5. Distributions of the major and minor axes of the hair diameter. The major and minor axes of the hair diameter were measured with 8926 fibers from 132 volunteers, and the frequency profiles of the major and minor axes were obtained with a 10-µm interval. Closed circles with a solid line and open circles with a broken line show the data of the major and minor axes, respectively. � 0 ..._ � u C G) ::s D"' G) ... LL 16 N = 8926 fibers (from 132 volunteers) 12 8 4 0 u------....._ ____ ,..__ ___ ____.,__._._....-..;;::,.___...-.._,-.,,,.J 1.0 1.3 1.6 1.9 Ellipticity of hair diameter 2.2 Figure 6. Distribution of the ellipticity of the hair diameter (major axis/minor axis). The ellipticity of the hair diameter was calculated from the ratio of the major axis to the minor axis, and the frequency profile of the ellipticity was obtained with a 0.05-unit interval.