J. Soc. Cosmet. Chem., 22, 839-850 (December 9, 1971) Some Observations on the Hair Cuticle LESZEK J. WOLFRAM, Ph.D., and MARTIN K. O. LINDEMANN, B.S.* Synopsis--Some PHYSICO-CHEMICAL PROPERTIES of CUTICLE are described and cor- related to the function of the latter in the overall STRUCTURE of HAIR. Chemical analy- sis of the cuticular layer revealed significant differences in the amino acid composition of the cuticle and the cortex of the hair KERATIN. The cuticle is extensively crosslinked by cystine, is more hydrophobic than the cortex, and contains large quantities of serine, glycine, and proline. All this satisfactorily accounts for the function of the cuticle as a molecular sieve and a chemical barrier. INTRODUCTION It is not surprising that the lion's share of our present knowledge of mammalian hair structure has been derived from studies on wool, which as an industrial commodity commands the resources necessary for extensive biochemical and physical investigations. The similarity in morphology and chemical properties of mammalian fibers provides a sci- entifically acceptable rationale for regarding the results on wool as ap- plicable to all of them, although such generalization from a specific case can be misleading. For example, it has become customary to focus one's attention almost exclusively on the ultrafine structure and properties of the cortex, which is the dominant structural element of the wool fiber. However, the cor- tex appears to be more important in wool than it is in hair. Conse- quently, when one is concerned with the latter, the properties of the re- maining morphological components (epicuticle, cuticle, cell inembranes, medulla) should be taken more fully into account. In an attempt to do this, we are presenting here a brief discussion concerning the contribu- tion of the cuticle to some of the physico-chemical parameters of human hair. * Gillette Company Research Institute, 1413 Research Boulevard, Rockville, Md. 20850.

840 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MORPHOLOGICAL CHARACTERISTICS Perhaps the most significant experimental fact which we should bear in mind at the onset of this discussion is that hair, unlike wool, is sur- rounded not by one, but by several (7 to 10) layers of cuticle cells (Fig. 1). Each of the cells is approximately 0.5 /• thick. Thus, on the average, a hair is encased by a 4.0-/• thick band of cuticular material. As the number Figure 1. Transverse section of cuticle and cortex of an oriental hair. 1No contrast enhanc- ing treatment was used. Magnification, 10,000