CHEMICAL AND PHOTO-OXIDATIVE HAIR DAMAGE 387 50 40 30 20 10 600 h R 600 h L 500 h 300 h 200 h Oh , , 0.0 0.2 0.4 0.6 0.8 Normalized Distance, r/a, into Fiber Radius (center-to-edge) Figure 4. Radial distribution of the diffusion coefficients in a hair fiber. 1.0 and increased dye diffusion/uptake in the more severely oxidized/damaged peripheral region. (b) It may also be argued that besides increased oxidative damage in the fiber periphery, there is a concentration/location dependence, due to dye-strike on the surface and heavier dye uptake in the fiber periphery than in the fiber interior. Therefore, the diffusion coefficients may be concentration-dependent. The overall effect is likely to be a combination of the two effects. The plots of the concentration ratio C/C o as a function of location along the fiber radius (Figure 5) show a much more gradual diffusion gradient as we move from the edge into 1.0 0.8 0.6 0.4 0.2 0.0 600 h L 500 h 600 h R Oh 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Distance, r/a, into Fiber Radius (center-to-edge) Figure 5. Dye concentration ratio as a function of location in the fiber radius.

388 JOURNAL OF COSMETIC SCIENCE the center of the hair fibers. These curves correlate well with the dye concentration profiles and the micrographs. UV MICROSPECTROPHOTOMETRY We have used UV microspectrophotometry to characterize photodamage in hair (6). Typical UV absorbance profiles at 340 nm of an untreated and UV-exposed fiber are shown in Figure 6a,b. The absorbance profile of the 300-hour photo-oxidized fiber shows that the photo-oxidized products are formed throughout the fiber cross section, with higher concentrations at the periphery. The profiles resemble the microfluorometric scans, suggesting that the photo-oxidized proteins are responsible for the increases in diffusion coefficients, thus supporting the microfluorometric approach adopted in this study. ELECTROPHORESIS Extractable proteins of unaltered and oxidized hair. The goal of electrophoretic separation was to determine oxidative damage to the main classes of proteins of unaltered hair modified by cosmetic chemical treatments, light exposure, and combinations of these processes. The molecular weights of the matrix proteins are in the range of 10 to 30 kDa, and those of the intermediate filament (microfibril) proteins are in the 40-55 kDa range (7). First, this study investigated the extractable main classes of proteins of unaltered as well as chemically and photochemically altered hair. In the case of oxidized hair, decreases/ increases in the amount of extractable proteins of a particular molecular weight, which are observed in untreated hair, suggest that these proteins were modified by chemical/ photochemical treatments. The occurrence of new protein bands not observed in un- treated hair is indicative of treatment-induced breakdown of proteins that had originally not been extractable. On the other hand, the absence of protein bands in treated hair, which were observed in untreated hair, suggests further crosslinking of the protein network, making it less soluble and therefore less extractable. Electrophoretic separation patterns are shown in Figures 7 and 8. This work shows that perming and UV irradiation may crosslink and/or fuse the matrix and intermediate-filament proteins, turning them into insoluble and, therefore, less extractable high-molecular-weight proteins. Long-term bleaching with peroxide and the use of bleaching/perming combinations, on the other hand, appear to degrade the matrix, intermediate-filament, and high-molecular-weight proteins, predisposing them to accelerated solubilization and extraction. These conclusions are based on Figures 7 and 8. Figure 7 clearly shows the effect of chemical and photochemical treatment on hair proteins. Lanes 1 and 10 show typical protein bands of the broad range standard. Lane 2 shows most of these protein bands as well, but at negligible concentrations. These are the typical protein bands of unaltered hair. The extractable amount of the matrix and intermediate-filament proteins significantly decreases with increasing exposure to UV radiation (lane 3 = 100 h lane 4 = 200 h lane 5 -- 300 h). In the case of the intermediate-filament proteins, extraction is completely