330 JOURNAL OF COSMETIC SCIENCE Table I Amino Acid Compositions for the Outer and Inner Halves of Curved Japanese Hair Fibers and for the Ortho- and Paracortical Cells of Wool Fibers (moles percent) Curved human hair Wool (Present work) (Average data of refs. 14-16) Amino acids Outer Inner �t P+ Ortho Para �t Asp 5.7 5.5 0.2 ** 6.7 6.2 0.5 Thr 6.9 6.8 0.1 *** 6.4 7.2 -0.8 Ser 11.8 11.8 0.0 10.3 10.6 -0.3 Glu 13.7 13.3 0.4 ** 13.1 12.7 0.4 Pro 7.6 7.8 -0.2 6.8 7.7 -0.9 Gly 5.7 5.6 0.1 * 8.2 7.4 0.8 Ala 4.6 4.6 0.0 5.8 5.6 0.2 Cys 15.8 17.0 -1.2 *** 9.8 11.4 -1.6 Val 5.6 5.5 0.1 5.7 6.0 -0.3 Met 0.4 0.4 0.0 0.4 0.3 0.1 Ile 2.8 2.8 0.0 3.4 3.5 -0.1 Leu 6.4 6.3 0.1 * 7.8 7.1 0.7 Tyr 1.9 1.8 0.1 2.8 2.5 0.3 Phe 1.7 1.6 0.1 2.8 2.5 0.3 Lys 2.6 2.6 0.0 2.7 2.4 0.3 His 0.9 0.9 0.0 0.6 0.5 0.1 Arg 5.9 5.9 0.0 6.9 6.4 0.5 t � = (outer - inner) or (ortho - para). + p means p-values obtained from the paired Student's t-test between "outer" and "inner" *p 0.05 **p 0.01 ***p 0.001. references (14-16), are also shown in the same table for comparison. In these references, the ortho- and paracortical cells of wool fiber were separated and applied on amino acid analyses. Differences in each amino acid between the outer and inner halves and between the ortho- and paracortical cells are shown as "Ll" in this table. The p-values obtained by the paired Student's t-test are summarized as "p" for the curved human hair. The differences (Ll) in amino acids between the outer and inner halves of curved human hair were relatively small, compared with the differences between ortho- and paracortical cells of wool fiber, as shown in Table I. In the case of wool fiber, the analyzed ortho- and paracortical cell samples were separated and purified before amino acid analyses. On the other hand, the divided half fiber of curved human hair is considered to be a mixture of at least two types of cortical cells and cuticle cells, but the major components of the outer- and inner-half fibers are probably ortho- and para-like cortical cells, respectively. The purity of each cell type in each half fiber was, therefore, possibly lower than that of each cell sample of wool. The lower purity of the cell type in the divided human hair is possibly the reason for the smaller differences in the amino acids between the outer and inner halves of curved human hair. Although the differences in curved human hair are smaller than those in wool, we compared the tendency of the differences in curved human hair and wool fibers. In Table I, the outer-fiber half of curved human hair shows the tendencies of more aspartic acid, threonine, glutamic acid, glycine, valine, leucine, tyrosine, and phenylal­ anine less praline and much less cysteine. Interestingly, these tendencies of curved

HAIR CURVATURE IN JAPANESE WOMEN 331 human hair are similar to the differences (Li) in amino acids between the ortho- and paracortical cells of wool fiber, except for the differences in threonine and valine. The differences in the amino acid composition of wool are partially explained by the results of gene expression in the wool follicle (8,17). Ultra-high sulfur keratin-associated pro­ teins are expressed preferentially in the paracortical cells, and high glycine-tyrosine keratin-associated proteins in the orthocortical cells. It is reasonable, therefore, that the paracortical cells show more cysteine and that the orthocortical cells show more glycine and tyrosine. In the case of the human hair follicle, an asymmetrical gene expression is observed in one of the high glycine-tyrosine keratin-associated proteins (18). The dif­ ferences in glycine and tyrosine in curved human hair may reflect the asymmetric gene expression, although the relationship between the asymmetrical gene expression and hair shape has not yet been clarified. The above results and discussion also suggest the similarity between curved human hair and crimped wool fibers. CONCLUSIONS 1. It was confirmed that 53% of Japanese women have straight hair, while the remaining 47% have curved hair, from slightly wavy to frizzy. The average curl radius of the hair of Japanese women was measured to be 4.4 ± 2.3 cm. The curl radius was widely distributed in the range of 0.6 to 16 cm. 2. TEM observation of typical highly curved hairs (curl radius: 0.6-1.0 cm) revealed an inhomogeneous internal structure. The structural difference between the outer and inner halves of curved hair was observed to be similar to that between the ortho- and para­ cortical cells of wool fibers. The three-dimensional structure of intermediate filaments (IFs) in the curved hair is, however, still unclear. 3. Amino acid analyses revealed the significant differences in half-cystine and acidic amino acid compositions between the outer and inner halves of curved hair. The dif­ ference in amino acid composition is also similar to that between the ortho- and para­ cortical cells of wool. The difference in amino acid composition strongly suggests differences in the protein composition between the outer and inner halves of curved human hair. The similarities between human hair and wool fiber in the TEM observa­ tions and the amino acid analyses suggest the possibility of a common or universal structure in curved mammalian hair. ACKNOWLEDGMENTS The authors express their sincere thanks to Dr. Warren G Bryson, formerly of Canesis Network Limited, for his helpful and fruitful discussions and for editing this manu­ script. Our sincere thanks are also due to Ms. Hiromi Shimogaki for technical support in the TEM observations. REFERENCES (1) C.R. Robbins, Chemical and Physical Behavior of Human Hair, 4th ed. (Springer-Verlag, New York, 2002), pp. 386-473. (2) A. J. Swift, "Morphology and Histochemistry of Human Hair," in Formation and Structure of Human Hair, P. Jolles, H. Zahn, and H. Hocker, Eds. (Birkhauser Verlag, Basel, 1997), pp. 149-175.