HAIR LIPID COMPOSITION 15 which is attributable to preventing external materials from entering into hair fibers as is the case in skin. Consequently, higher levels of endogenous lipids in group B may result in diminished levels of exogenous ones due to their difficulty in penetration, while lower levels of endogenous lipids in group B may result in increased exogenous ones in hair fibers. Available studies dealing with lipids within human hair have hitherto used the term "internal lipids" for lipids within hair fibers (6, 7, 11-20). This term for lipids penetrat­ ing from a sebaceous gland into hair fibers may be not misdirected because these lipids are internalized. However, based upon the fact that they are not intrinsic internal lipids, they should be designated as exogenous lipids (group A), as revealed in this study. On the other hand, endogenous lipids consisting of CH and CERs (group B) and MEA (group D) should be designated as intrinsic internal lipids of human hair. While some F As originate from hair matrix cells, most F As may occur as a result of the decompo­ sition of TGs or WEs as sebum components. This is corroborated by the fact that there are higher levels of unsaturated and branched FAs in hair lipids (7,18,28) and that there is the positive correlation between FAs and the other exogenous lipids. Therefore, it is likely that a lipid class of FAs within hair fibers occurs mainly as exogenous lipids. CONCLUSION In summary, the lipid composition at the proximal root regions of human hair has been characterized for the first time. The hair lipids can be classified into four groups: group A (SQ, WEs, TGs, and FAs) group B (CH and CERs) group C (HCs) and group D (MEA). Since group A or groups B and D originate from sebum penetrating the hair shaft or from constitutive hair lipids biosynthesized in hair matrix cells, they were designated exogenous lipids or endogenous ones, respectively. The hair lipid composi­ tion among individuals was also characterized by a predominant negative correlation between lipids for groups A and B. This negative correlation suggests that the endog­ enous lipids in group B serve as a barrier against the penetration of exogenous lipids (group A). Although many researchers have hitherto used the term "internal lipids" for all hair lipids including exogenous lipids (group A in our study), only endogenous lipids consisting of CH and CERs (group B) and MEA (group D) should be designated as intrinsic internal lipids of human hair. ACKNOWLEDGMENTS We express our cordial gratitude to Dr. Yoshiaki Fujikura and Dr. Katsumi Kita for their discussions and encouragement of this study. Our sincere thanks are also due to Mr. Toshihiko Sakai and Ms. Kumi Sugino for their assistance in hair sample collections. REFERENCES (1) J. A. Swift and A. W. Holmes, Degradation of human hair by papain. Part 2: Some electron micro­ scope observations, Text. Res.]., 35, 1014-1019 (1965). (2) S. Naito, T. Takahashi, M. Hattori, and K. Arai, Histochemical observation of the cell membrane complex of hair, Sen-I Gakkaishi, 48, 420--426 (1992). (3) J. D. Leeder, The cell membrane complex and its influence on the properties of the wool fibre, Wool Sci. Rev., 63, 3-35 (1986). (4) A. Korner, S. Petrovic, and H. Hocker, Cell membrane lipids of wool and human form liposomes, Text. Res.]., 65, 56-58 (1995).

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