374 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS • •.. • --. •_ • - • - . • . '• • • . - ':- •e -" • ,• • •" • - '• • , ' "' .• • •" •"'• • . 2.. • '•' '•*' --' • '• " " . .:•,_ . • . • .... ' ' . •.•* '" , , . • •,.• ,•' . • •. ? . • .•,. •, •,. .. ., • . . . . •.•.. Figure 10. Transmission electron micrograph of longitudinal section of Caucasian beard hair. Magnifica- tion 2750x. 2. Mechanical Properties The tensile properties of Caucasian beard and scalp hair in water, at 21øC, are summarized in Table V. The lower elastic modulus of beard is probably due to both the lower level of disulfide bonding (as shown later in this paper) and the higher degree of medullation. 3. Chemical Characterization a. Amino Acid Composition The amino acid profiles of Caucasian facial and scalp hair (Table VI) showed a significant difference in the cystine content, which was about 18% lower in beard hair.

COMPARISON OF BEARD AND SCALP HAIR 375 This result was somewhat unexpected, considering the fact that beard hair has more cuticular layers which are rich in cystine (5). The overriding factor is presumably the relatively high level of medullation in beard hair, since medullary cells were shown to have very little cystine but higher levels of basic, acidic, and aromatic amino acids (20-21). It is, however, also possible that the cystine level of the cortical cells of facial and scalp hair is different. Beard hair was also found to be richer in aspartic acid, lysine, and tyrosine and poorer in threonine, serine, and valine. Figure 11. Transmission electron micrograph of longitudinal section of Caucasian beard hair without medullation. Magnification 915 x.