PHOTODEGRADATION OF HUMAN HAIR 117 Transmission Intensity (%FS) 60 50 40 30 20 10 0 o I 4 Peroxide Treatment (h) Transmission Intensity (%FS) 60 40 20 0 100 300 500 700 QUV Exposure ( hours ) Figure 11. Comparison of loss in hair color due to chemical oxidation with 6% alkaline hydrogen peroxide (top) and UV irradiation (bottom). degradation not only of the cuticula and melanin granules, but also of the hair fiber in general. Optical microscopy. The unusual results demonstrated in the SEM study produced several questions about the drastic changes in the physical nature of the fiber's topography. Therefore, long-term UV-irradiated hair fibers were observed in the optical microscope during alkaline peroxide treatments, which provided some answers to questions about

118 JOURNAL OF COSMETIC SCIENCE 006020 5. 0 RV xG00 50. O•,mtl. doGo 1 kV x 5 ß B. Figure 12. Longitudinal (a,b) and cross-sectional (c,d) views of long-term UV-irradiated hair fibers after subsequent 15-rnin treatment with 6% alkaline hydrogen peroxide. this extreme cuticular disintegration during chemical oxidation of UV-exposed fibers. Long-term UV irradiation causes extensive oxidative degradation of the proteins of the cuticula as manifested in an Allw6rden-like reaction during subsequent chemical oxi- dation of UV-exposed hair fibers (Figure 14a-f). After only seconds of alkaline peroxide treatment (Figure 14b,c), small bubbles develop along the hair surface. These small bubbles or half domes resemble the famous Allw6rden sacs formed by the Allw6rden reaction. Allw6rden first detected these sacs at the surface of wool fibers during treat- ment with chlorine water. He thus also discovered the epicuticle surrounding the cuticle cell. The epicuticle is a semipermeable, partly proteinaceous membrane, -25 A in thickness, which allows small molecules (water) to diffuse into the cell, rapidly swelling degraded, hydrophilic, low-molecular-weight peptide fractions. The highly hydrophilic molecules are not capable of diffusing out and remain trapped inside the cell. In Allw6rden's reaction, the hydrophilic molecules continue to attract water from the outside solution, and thus these sacs are formed by the resulting osmotic pressure. In our study concerning long-term UV exposure of human hair, the bubbles resembling Allw6rden sacs are formed by diffusion of peroxide, ammonium hydroxide, and water through the epicuticle into the cuticle cell, where the already photolytically degraded proteins are now further degraded by the peroxide and swollen by water. The hydrophilic protein fractions are still too bulky to diffuse out through the semipermeable epicuticle. They remain trapped within the cuticle cell, attracting water and forming the sac-like