Hair Ethnicity 198 Chemical Structures Having briefly reviewed some of the theories and results related to the biology of hair, differences that may be related to the curliness of hair and/or ethnicity will be discussed. As described in Chapter 1 of this book, the hair consists of mostly protein with small amounts of lipids and water. Investigations into the potential differentiation of the cells of the cortex, followed by the proteins that they are comprised of, and finally the amino acids and lipids are discussed herein. Several studies have examined the internal structure of hair as it pertains to curliness. The early investigation of the differences in hair properties by racial classification often compared African, Asian, and Caucasian hair, and/or wool.1,19,20 Differences were observed but were relatively inconsistent. In relation to the distribution of cortical cells, Mercer reported a bilateral distribution in African hair however, subsequent work indicated that, if present, it was relatively insignificant as compared to that found in wool.1 Spearman and Barnicot supported the lack of a bilateral distribution of cortical cells in human hair based on a study conducted in the early 1960s.21 Contrary to the earlier findings, studies conducted decades later revealed the existence of both para- and ortho-cortical cells.22-24 A study of straight and curly Japanese hair examined longitudinal sections of the hair to compare the inner and outer sections as oriented to the natural curl of the hair. Examination of micrographs and the results from chemical analysis implied a bilateral distribution of cortical cells, similar to that seen in wool.23 The intermediate filaments (IFs) were smaller and dispersed in the matrix on the outer portion of the fiber, while appearing larger and fused together on the inner portion. Amino acid comparison of these portions revealed that the outer section contained more aspartic acid, glutamic acid, threonine, glycine, valine, leucine, tyrosine, and phenylalanine, with lower amounts of cystine. These results are in line with previously reported differences in amino acid content for ortho- and para- cortical cells. No such differences were observed for the longitudinal sections of the straight hair. A study of straight, wavy and curly hair