116 JOURNAL OF COSMETIC SCIENCE Figure 10. Intact (a) and partially (b,c) and completely (d) solubilized melanin granules before and after 1 h and 4 h of oxidation with 6% alkaline hydrogen peroxide, respectively. hair fibers (cuticle cells and melanin granules) and preconditioned them further to accelerated disintegration. After one and two hours of alkaline peroxide bleaching of long-term UV-irradiated hair fibers, the cuticula has completely disintegrated and dissolved into an unrecognizable, thin, film-like layer of cuticular membranes enveloping the outer cells of the cortex (Figure 13a,b). The disintegration, dissolution and fusion of the cuticle cells are so advanced that the individual cuticle cells are no longer identifiable. The original to- pography of the hair fiber no longer exists. Instead of surface cuticle cells with their characteristic scale-like structure, a bumpy surface covered by a thin film is displayed. This thin film may consist of cuticular remnants, the cell membranes, and the CMC, which exists between cuticula and cortex. The corresponding cross-sectional views of these fibers demonstrate the progressive damage inflicted upon the hair fiber by long- term UV exposure, (Figure 13c,d). The low magnification cross section (Figure 13c) shows the fused cuticula and merely a cortex containing empty cavities (Figure 13d) where once the melanin granules were housed. Besides severe oxidative damage to the cuticula, long-term U¾ irradiation has also photochemically degraded the melanin granules, and has preconditioned them for accelerated dissolution during subsequent short-term treatment with alkaline hydrogen peroxide. These observations clearly show that long-term UV exposure causes severe chemical

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