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]. Cosmet. Sci.! 59, 317-332 Quly/August 2008) Characterization of curved hair of Japanese women with reference to internal structures and amino acid composition SHINOBU NAGASE, MASARU TSUCHIYA, TOSHIHIKO MATSUI, SATOSHI SHIBUICHI, HISASHI TSUJIMURA, YOSHINO RI MASUKA WA, NAOKI SATOH, TAKASHI ITOU, KENZO KOIKE, and KAORU TSUJII, Beauty Research Center! Kao Corporation! 2-1-3! Bunka, Sumida-ku, Tokyo 131-8501 (S.N., M.T., T.M., S.S., N.S., T.I., K.K), Analytical Science Research Laboratories, Kao Corporation, 2606, Akabane, Ichikai, Haga, Tochigi 321-3497 (H. T., Y.M.), and Nanotechnology Research Center, Research Institute for Electronic Science, Hokkaido University, N-21, W-10, Kita-ku, Sapporo 001-0021 (K. T.), Japan. Accepted for publication February 20, 2008. Synopsis The variation of hair curvature in Japanese women was quantitatively investigated and the structure of curved hair was characterized with transmission electron microscopy (TEM) and amino acid analysis. Two hundred and thirty Japanese women volunteers, aged from 10 to 70 years, were randomly selected. The evaluation of the volunteers' natural hair shape showed that 53% of Japanese women have straight hair, while the remaining 47% have curved hair (varying from a slightly wavy shape to a frizzy style). The average curl radius of the volunteers' hair was determined to be 4.4 ± 2.3 cm, and ranged widely from 0.6 to 16 cm. The TEM observation of curved hair fiber revealed an inhomogenous internal structure between the outer and inner regions of the curved shape. In relation to the inhomogeneous structure of the curved hair, different amino acid composition of the hair keratin was observed between the outer and inner regions. Interestingly, these results of the TEM observation and the amino acid analysis are analogous to the difference between the ortho- and paracortical cells in wool fibers, suggesting the universal structure of curved mammalian hair. INTRODUCTION It is well known that the scalp hair shape of East Asian people, including the Japanese, is predominantly straight in appearance when compared with that of Wes tern and African people (1), but more careful observations reveal that the hair shape of Japanese people can vary from straight to wavy. A certain number of Japanese women have a mixture of hair fiber types, varying from straight to curved, with some meandering hairs. 317