JOURNAL OF COSMETIC SCIENCE 460 or fusion reactions similar to long-term irradiation effects on wool fi ber, as explained in the next section of this review (90). For hair damaged by sunlight, in most cases, the lipids of the cuticle–cuticle CMC sometimes appear altered to a greater extent than the more susceptible areas of the cortex–cortex CMC because the outer layers of the fi ber re- ceive higher intensities of radiation. SHORT-TERM IRRADIATION ATTACKS CMC LIPIDS, PRODUCING INTERNAL STEP FRACTURES Fracturing of wool fi ber exposed to simulated sunlight has been studied microscopically by Zimmermann and Hocker (90). Electron micrographs of human hair fi bers exposed to simulated sunlight and then fractured, showing that human hair provides similar effects to those of wool fi ber, have been provided to this author by Sigrid Ruetsch. Zimmerman and Hocker demonstrated that stretching nonirradiated control wool fi bers in water provided primarily smooth fractures, while short and intermediate times of simulated sunlight exposure caused the fi bers to break mainly as step fractures. These scientists suggested that short- and intermediate-term irradiation damages the lipids of the CMC (all three types of CMC) and thereby provides many internal step-type fractures by axial propagation of cracks through the photochemically damaged cortex–cortex CMC. Longer-term irradiation creates crosslinks in the hair, fusing it and creating amorphous fractures. Thus, short- and intermediate-term irradiation attacks CMC lipids, providing for in- creased beta-delta failure in the cuticle–cuticle CMC and multiple step fractures in the cortex–cortex CMC. Longer-term irradiation produces amorphous fractures by fusion re- actions through the creation of carbonyl groups that are cross-linked through lysine groups, analogous to the oxidative damage to proteins and mitochondrial decay associ- ated with aging, as described by Dean et al. (91). These fusion reactions start in the pe- riphery of the fi ber, where it receives higher intensities of radiation than the core, providing a smooth fracture at the periphery and multiple step fractures in the interior of the fi bers and, if exposed long enough to light radiation, amorphous fractures are pro- duced across the entire fi ber. Short- and intermediate-term exposures to radiation are propagated by abstraction of hydrogen atoms from tertiary carbon atoms of 18-MEA (89) and of allylic hydrogen at- oms of oleic and palmitoleic acids in free lipids of the cuticle–cuticle CMC. The cortex– cortex CMC contains tertiary hydrogen atoms on cholesterol and cholesterol sulfate and allylic hydrogen atoms on oleic and palmitoleic acids, and on cholesterol and cholesterol sulfate, which react similarly. The abstraction of hydrogen atoms from tertiary carbon atoms on amino acid side chains (analogous to the tertiary carbon atoms on 18-MEA and cholesterols) has been shown by Goshe et al. (92) to predominate over the abstraction of hydrogen atoms at the alpha carbon atom of amino acids in polypeptides. This fact helps to explain why the beta layers are degraded faster by photo-oxidation than the hair proteins via the cross-linking fusion reactions and why step fractures are produced on short- and intermediate-term radiation exposures, while amorphous fractures are produced only after longer-term exposures. Hoting and Zimmermann (88) have also demonstrated that the CMC lipids of the cortex of hair, previously bleached with peroxide-persulfate, are more readily degraded by radiation

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,