112 JOURNAL OF COSMETIC SCIENCE 30509• 5•0 kV x4.0•k"'ff25•'•& .. Figure 6. a-d: Typical longitudinal views of a long-term UV-exposed hair fiber, displaying severe radial cracking, a typical radiation-induced damage phenomenon. tected from degradation, which, in turn, prevents a loss of hair color. The assumption was made that photochemical oxidation of the melanin chromophor would have to occur in situ if color loss was to occur at all. This is quite in contrast to the swelling and dissolution of the melanin granules by chemical oxidation with hydrogen peroxide. After 1 hour of oxidation with 6% alkaline hydrogen peroxide, moderate disintegration of the melanin granules had occurred (Fig- ure 10b,c). The subgranular structures, which make up the melanin granules, appear more pronounced. There are various stages of degradation, from mile to severe, due to partial solubilization of the melanoprotein. Solubilization appears to occur preferentially from the center of the granules (Figure 10c). After the hair fibers were exposed for four hours to oxidation with 6% alkaline hydrogen peroxide, most of the granular cavities were empty (Figure 10d). The assumption was made that the majority of the cavities were empty because the granules were dissolved away by the peroxide. Progressive solubilization of the melanoproteins is the prerequisite for solubilization and/or dispersion of the melanin pigments. With the melanoprotein dissolved and diffused into the bulk of the hair fiber, the spread-out melanin pigment becomes the unrestricted target of bleaching or loss in color of the human hair. Wolfram and Hall (10) have observed similar behavior with melanin granules isolated from hair and exposed to peroxide bleaching.

PHOTODEGRADATION OF HUMAN HAIR 113 Figure 7. a-d: The "cathedral spire" fracture pattern seen upon extension of hair fibers exposed to 700 h of UV irradiation/humidification cycling. Using microspectrophotometry, we have shown that under the selected conditions of progressive exposure to UV radiation/humidification cycling in the QUV, no or insig- nificant loss of color occurs after short exposure times and that only moderate lightening of the color is observed after 700 hours of UV exposure. The melanin granules remain intact as observed in the FESEM. Chemical oxidation, on the other hand, results in increased lightening of the hair color with increased exposure time, while solubilization of the melanin granules occurs. Since microspectrophotometry is a non-destructive technique, the change in hair color is measured in transmitted light at the very same (previously marked) locations on the very same hair fibers under identical instrumental settings before and after the various exposure times to UV radiation. Increases in transmission intensity are directly propor- tional to loss in hair color. The same technique is used on hair fibers exposed to chemical oxidation. Figure 11 compares the decrease in hair color caused by chemical oxidation with 6% alkaline hydrogen peroxide versus progressive UV irradiation. MANIFESTATION OF ADVANCED UV DEGRADATION OF HAIR PROTEINS (CUTICULA AND MELANIN GRANULES) DURING SUBSEQUENT HYDROGEN PEROXIDE TREATMENT Hair fibers exposed to long-term (700 h) UV irradiation/humidification cycling, and