CELL MEMBRANE COMPLEX 461 than the lipids of chemically unaltered hair or the lipids of hair dyed with a red oxidation dye. This conclusion was reached by analysis of the cholesterol-containing lipids of hair that reside primarily in the cortex–cortex CMC (Figure 3). Peroxide-persulfate oxidation of hair is primarily a free-radical oxidative process and it leaves hydroperoxide groups in the hair in the CMC and in other regions. Thus the action of sunlight on peroxide- persulfate bleached hair (containing hydroperoxides) makes the hair more vulnerable to cuticle fragmentation and to splitting effects that the CMC plays a signifi cant role in. In this same paper these scientists demonstrated that one red oxidation dye provides photoprotection to both UV-A and visible light but not to UV-B light when compared to chemically untreated hair, and therefore retards the degradation of the CMC lipids, most likely by the dye acting as a radical scavanger. LIPIDS REMOVED FROM HAIR BY PERMANENT WAVING Hilterhaus-Bong and Zahn (93) and Mahrle et al. (94) independently showed that part of the lipid components of the CMC were removed from hair by permanent waving. Hilterhaus-Bong and Zahn examined internal hair lipids from permanent-waved hair versus non-waved hair by extraction with chloroform/methanol (internal lipids of the cortex–cortex CMC) and found signifi cantly less internal lipid in permanent-waved hair permed at neutral pH and even less internal lipid in hair permed at pH 9. PENETRATION INTO HAIR AND THE CMC In 1983, Leeder and Rippon (95) described the effects of formic acid on the dyeing of wool fi ber and concluded that formic acid removes labile lipid and non-keratin proteins from the CMC. These scientists described that formic acid is an excellent swelling me- dium for keratin fi bers and applied Zahn’s swelling-factor calculations (96) to the amino acid analysis of the CMC, from which they estimated that the CMC is swollen to a very large degree by formic acid (97). They also described that formic acid modifi es the CMC and has a greater effect on the sorption of n-propanol than surface degradation treatments, and they therefore concluded that the CMC is an “alternative to the cuticle” for the penetration of dyes into keratin fi bers. Naito et al. (98), in 1992 suggested that the delta layer provides a pathway for hydrophilic ingredients to penetrate into hair. Swift (99) and Inoue (52) have provided additional evidence that the CMC and endocuticle are pathways for diffusion of molecules into hair. Kreplak et al. (100) have shown by microbeam X-ray diffraction that the delta layer of the cuticle–cuticle CMC swells about 10–15% in water, and therefore, although it is hydrophilic, it is not as hydrophilic as originally thought nevertheless, it still can serve as a pathway for diffusion of hydrophilic ingredients into hair. In addition, when the CMC or endocuticle have been weakened or damaged, the hair is even more penetrable to dyes and other chemicals through the CMC (52). THE CMC OF WOOL FIBER VS HUMAN HAIR To date, I could not fi nd any references comparing the CMC of wool fi ber versus human hair wherein signifi cant structural or reactivity differences have been cited. As of this writing it would appear that the primary differences lie in the number of cuticle layers,

JOURNAL OF COSMETIC SCIENCE 462 which relates to the amount of cuticle-to-cuticle overlap and to the relative amounts of cuticle–cuticle CMC versus cuticle–cortex CMC versus cortex–cortex CMC. The Allworden reaction can be produced on both wool fi ber and human hair (29). Although the reaction appears different on human hair than wool fi ber, Bradbury and Leeder (15) have shown that this is because of much greater scale overlap on human hair, where only about 1/5th to 1/6th of each cuticle cell shows on the surface of hair fi bers, and they explain that Merino wool contains only a single layer of cuticle scales, with approximately 5/6th of each scale in the surface and only about 1/6th scale overlap (29) on the surface. Individual cuticle cells have also been isolated from wool, human hair, and several other keratin fi bers, and have been shown to behave similarly to chlorine water (29). 18-MEA accounts for 40–50% of the covalently bound fatty acids in human hair and wool fi ber (35) and it is at- tached to the top surface of cuticle cells in both fi bers (11). Table I shows that the covalently bound fatty acids are similar in both human hair and wool fi ber and that covalently bound fatty acids are in the cuticle–cuticle CMC but not in the cortex in both of these fi bers. The compositions of the solvent-extractable lipids of both fi bers are similar, consisting primarily of fatty acids, cholesterol, cholesterol sulfate, and ceramides (34,35). Further- more, these lipids are extractable from both human hair and wool fi ber with chloroform/ methanol/aqueous potassium chloride, and liposomes can be generated from these ex- tracts (48). Furthermore, these extracted lipids represent the main ingredients in the cortex–cortex CMC, and they are very similar in both fi bers. And last, but not least, the effects of chemical and photochemical reactions and physical stresses are similar for the CMCs of both of these fi bers, as shown in “Chemical and Physical Actions on the CMC of Hair,” in this review. Perhaps, with additional research, signifi cant structural and/or re- activity differences between the CMCs of human hair and wool fi ber will become more apparent, but they are not apparent today. REFERENCES (1) G. E. Rogers, Electron microscope studies of hair and wool, Ann. N.Y. Acad. Sci., 83, 378–399 (1959). (2) G. E. Rogers, Electron microscopy of wool, J. Ultrastruct. Res., 2, 309–330 (1959). (3) R. D. B. Fraser, T. P. MacRae, G. Rogers, et al., in Keratins: Their Composition, Structure and Biosynthesis, I. N. Kugdmass, Ed. (C. C. Thomas, Springfi eld, Ill., 1972), Ch. 4. (4) C. Robbins et al., Failure of intercellular adhesion in hair fi bers with regard to hair condition and strain conditions, J. Cosmet. Sci. 55, 351–371 (2004). (5) W. G. Bryson, B. R. Herbert, D. A. Rankin, and G. L. Krsinic, Characterization of proteins obtained from papain/dithiothreitol digestion of Merino and Romney wools, Proc. 9th IWTRC, Biella, Italy, 1995, pp. 463–473. (6) A. J. Swift and J. Holmes, Degradation of human hair by papain. III. Some electron microscope ob- servations, Textile Res. J., 35, 1014–1019 (1965). (7) A. J. Swift, Human hair cuticle: Biologically conspired to the owner’s advantage, J. Cosmet. Sci. 50, 23–47 (1999). (8) Y. Nakamura et al., Electrokinetic studies on the surface structure of wool fi bres, Proc. 5th, IWTRC, Aachen, 5, 34–43 (1975). (9) R. D. B. Fraser, T. P. MacRae, and G. E. Rogers, in Keratins: Their Composition, Structure and Biosynthesis, I. N. Kugdmass, Ed. (C. C. Thomas, Springfi eld, Ill., 1972), pp. 70–75. (10) L. N. Jones and D. E. Rivett, Effects of branched chain 3-oxo acid dehydrogenase defi ciency on hair in maple syrup urine disease, J. Invest. Dermatol., 104, 688 (1995). (11) L. N. Jones and D. E. Rivett, The role of 18-methyleicosanoic acid in the structure and formation of mammalian hair fi bers, Micron, 28, 469–485 (1997).