HAIR LIPID COMPOSITION 11 Table II Correlation Coefficients for the Levels of Each Lipid Among Individuals 1 Correlation coefficient Lipid HCs SQ WEs TGs FAs CH CERs SQ -0.1815 WEs -0.2232 0.7386** TGs 0.0410 0.2421 0.2123 FAs 0.0463 0.4879** 0.3942** 0.0718 CH -0.1404 -0.5353** -0.6133** -0.4422** -0.6479** CERs -0.3378* -0.3260* -0.4516** -0.3263* -0.5019** 0.7716 MEA 0.1640 -0.1565 -0.1240 -0.2219 -0.1171 0.2172 0.1130 1 0.2 mg/g hair was calculated as = 0. ** p 0.01 *p 0.05. Abbreviations: as described in Table I. phrase "precise hair lipid composition" means the hair lipid composition that is not changed by any external factors such as weathering (shampooing, heat, light, and so on), perming, or coloring. In all past studies, hair samples were not from the proximal root ends or were not precisely identified for sites of the hair shaft collected (6,7 ,11-20). In this study, only the 5-cm length from the proximal root end of hair fibers was used, and the hair lipids without contaminated lipids were obtained by extraction with CH 3 Cl/ CH 3 OH/water and with 1 N KOH in 90% CH 3 OH following 5-min hexane incubation after shampooing. In our comprehensive analysis of hair lipids at the proximal root regions of hair fibers from 44 Japanese females, the average content of total hair lipids was 23.5 mg/g hair, comprising 2.4, 0.7, 4.9, 0.5, 14.4, 1.3, 0.29, and 0.30 mg/g hair for HCs, SQ, WEs, TGs, FAs, CH, CERs, and MEA, respectively (Table I). The level of each lipid showed a great fluctuation among individuals (Table I), suggesting that the hair lipid composition of human hair varies considerably among individuals. The molecular species of CERs identified in Japanese females (Figure 1) were almost the same as those identified in Caucasian males, as reported by Hussler et al. (19). Thus, hair CERs belonged to class 2 or class 5 according to the ceramide classification reported for the stratum corneum (27). However, the content of hair CERs determined in our study (average 0.29 mg/g hair) was much higher than that reported by Hussler et al. (average 0.1 mg/g hair) (19). The difference between the content of hair CERs in those two studies might be due to different sample origins as described above, although it might also result from other factors such as different races and/or gender of the subjects, and/or hair diameter/volume per cm length. The results from the relationships among the levels of lipids indicate that the hair lipids may be tentatively classified into the following four groups: group A (SQ, WEs, TGs, and F As) group B (CH and CE Rs) group C (HCs) and group D (MBA). While each lipid level in group A or each lipid level in group B is positively correlated with each other, each lipid level in group A is negatively correlated with each lipid level in group B (Figure 7, Table II). Since the level of HCs or MEA did not correlate in most cases with each level in other lipids, HC and MEA were classified into the other groups (group C and group D). The PCA showing the total variation of hair lipids among 44 indi­ viduals indicates that the hair lipid composition can be especially characterized by a negative correlation of each lipid level between group A and group B, which predomi-

12 JOURNAL OF COSMETIC SCIENCE 20 ------------- 5 A R=0.7386 P0.01 • . . . • . •· . .. .........•···....•··...•.··.........•··········•.......•···········.•• . • • • • 0 ----"'---......ii.....--....i...--......1 0 1 2 3 SQ mg/g hair 4 0.6 --------------- � 0.2 � u B R=0.7716 P0.01 . . ..... • •• ,: . . ....·.....•·· . • • • . •· ..•·... .... •·� . •,... •· . . ....... . ·.•....• .. ····•••·· ... •· . . • • • • • • 0 . 0 ..__ ____ .,__ ____ .,__ _______. 0 1 2 CH mg/g hair 3 3-------------- ..... � 2 = 1 u • •. • C R= -0.6133 P0.01 • • • •···· - .. , .. ··· ····•.. .• . .:. ... . : ····· ·�·•. . . . . . ·• .. • . . ··•.. . • . . .... ··· • .... . 0 ._ __ ..._ ______ ......., __ ___. 0 5 10 15 WEs mg/g hair 20 Figure 7. The relationship between the levels of lipids from 44 Japanese females. Each point represents the level of the lipids for each individual. A: SQ and WEs. B: CH and CERs. C: WEs and CH.