HAIR LIPID COMPOSITION 13 Table III Factor Loading, Eigenvalue, Contribution, and Accumulated Contribution for Principal Components of Eight Lipids Lipid First Second Third HCs -0.022 0.728 0.155 SQ -0.411 -0.310 -0.201 WEs -0.425 -0.293 -0.183 Factor TGs -0.253 0.003 0.558 loading FAs -0.381 0.160 -0.405 CH 0.500 -0.133 -0.089 CERs 0.421 -0.353 -0.120 MEA 0.118 0.346 -0.636 Eigenvalue 3.386 1.444 1.196 Contribution (%) 42.3 18.1 15.0 Accumulated contribution (%) 42.3 60.4 75.3 Abbreviations: as described in Table I. 4 2 0 0 0 0 8 � 0 0 8 0 0 0 0 0 0 0 0 0 0 0 -2 - 0 0 -4 -2 Component Fourth -0.130 0.065 0.040 0.737 -0.124 0.070 0.171 0.620 0.709 8.9 84.2 0 Zl 0 0 0 0 Fifth -0.469 -0.364 -0.476 0.159 0.600 -0.170 0.003 -0.081 0.539 6.7 90.9 0 0 0 0 o8 0 Sixth Seventh Eighth 0.388 0.209 0.116 0.539 -0.455 -0.245 -0.325 0.443 0.412 0.134 0.012 0.194 0.345 0.111 0.400 0.132 -0.403 0.715 0.508 0.613 -0.140 -0.199 -0.052 -0.170 0.415 0.187 0.122 5.2 2.3 1.5 96.1 98.5 100.0 0 0 0 Ooooo 0 O 2 4 Figure 8. Two-dimensional projection of 44 Japanese females by the first two components (21 and 22) of PCA for the levels of eight lipids. Each point (0) represents the values of 21 and 22 for each individual. nantly accounted for 42.3% of the total variation (Table III, Figure 8). Individuals whose hair fibers contain lower lipid levels in group A and higher lipid levels in group B are distributed at the right-hand side of the projection in Figure 8. In contrast, individuals whose hair fibers contain higher lipid levels in group A and lower lipid levels in group B are distributed at the left-hand side of Figure 8. Distribution of the younger and older individuals according to their ages in the PCA, as shown Figure 9, suggests that the hair lipid composition may change with increasing age. Since lipids in group A (SQ, WEs, TGs, and FAs) are components similar to those of sebu� (28), it is likely that the lipids in group A result from sebum attributable to

14 4 2 ◊ N □ N 0 • 1::t,. □ a -2 • -4 JOURNAL OF COSMETIC SCIENCE a .A. .A. � � ·2 a 0 1:,. 1::t,. □ -2 0 Zl ■ 1::t,. ◊ X .A. ■ a c:i 0 x• 0 oo-00a □ 0 2 4 Figure 9. Two-dimensional projection of 44 Japanese females by the first two components (Zl and Z2) of PCA for the levels of eight lipids. Each point represents the values of Zl and Z2 for each individual. Symbols: 0: ages 1 to 10. D: ages 11 to 20. 6: ages 21 to 30. e: ages 31 to 40. ■: ages 41 ro 50 . .&: ages 51 to 60. T: ages 61 to 70. x: ages 71 to 81. sebaceous glands. Thus, the lipids in group A may originate from sebum penetrating into the inside of hair fibers within hair follicles where sebaceous glands are included histologically. Koch et al. (15) designated hair lipids within hair fibers as "internal sebum" in their paper. Although some FAs may originate from hair matrix cells, the existence of higher levels of unsaturated and branched FAs in hair lipids (7 ,18,28) suggests that most FAs result from decomposition of TGs or WEs as sebum. On the other hand, lipids in group B (CH and CERs) are thought to result from intrinsic constitutive lipids biosynthesized in hair matrix cells, based upon the fact that they are not synthesized in sebaceous glands (28). HCs (classified into group C) consisting of carbon number 22-44 has been reported in the analysis of hair lipids (29), but their origin remains unclear. It has been proposed by a study using Maple Syrup Urine Disease patients (6) that MEA (classified into group D) may result from an intermediary me­ tabolite of isoleucine within hair matrix cells. Therefore, according to their origins, group A can be designated as exogenous lipids and groups B and D as endogenous lipids. Changes in hair lipid composition with special reference to exogenous lipids with increasing age (Figure 9) could be explained in terms of increased sebum secretion during adolescence (30). The level of MEA did not correlate with both lipids in group B (CH and CERs), although these three lipids are endogenous. This suggests that the production of either CH or CERs may interact with each other during the biosynthetic process, while MEA may be regulated by another metabolism. The reason that there was a negative correlation between each level of exogenous lipids (group A) and endogenous ones (group B) might be due to the contribution of the CMC. Since endogenous lipids in group B are the main components of cell membrane lipids that form CMC (4,17), they can lead to the formation of stable and strong CMC. Therefore, stable and strong CMC may result in enhancing the barrier function (31,32),