54 JOURNAL OF COSMETIC SCIENCE a b Figure 6. Cross section of red hair (after irradiation and washing). a: After VIS-light irradiation. b: After UV-light irradiation. UV light was irradiated on hair under these experimental conditions, the pheomelanin began to decompose, which caused the red hair to lighten. On the other hand, eumelanin was hardly affected by the UV light irradiation and the blond hair did not therefore lighten. In the case of VIS-light irradiation, the degradation of melanin in blond hair was found to be a little higher than that of red hair however the difference was within the bounds of experimental error (Figure 5 ). From this, it is supposed that the two types of melanin are similarly sensitive to VIS light, or perhaps eumelanin is just a little more sensitive than pheomelanin. PHOTOLIGHTENING OF ISOLATED GRANULES FROM RED HAIR The isolated granules obtained from red hair are judged from their appearance to be pheomelanin however, they are possibly denatured through the papain treatment. The photolightening behavior of the isolated granules was also studied and compared with the results of the irradiated cross section. The photolightening behavior of the granules is shown in Figure 7. The degree of photolightening was a little higher for UV light than for VIS light. However, the difference is so small that we cannot say this is consistent with the much clearer result of the irradiated cross section, where the melanin remained chemically intact. This clarifies that pheomelanin, denatured by treatment with papain, is not suitable for the study of photosensitivity. CONCLUSIONS Both VIS and UV light lighten red hair. Unlike blond hair, washing after irradiation is

�L 12 10 8 6 4 2 0 0 PHOTOLIGHTENING MECHANISM OF RED HAIR 55 ---vis light - -o - UV light 10 20 30 40 50 60 70 80 90 100 irradiation units Figure 7. Lightening degree of the granules isolated from red hair. Solid line is the result of VIS-light irradiation. Dotted line is that of UV-light irradiation. not necessary for the lightening of red hair by UV light. The difference in the photo­ lightening behaviors of red and blond hair should be due to differences in their melanin types. It is proven that pheomelanin, which is predominant in red hair, is highly sensitive to UV light. In the cases of both red and blond hair, hair protein absorbs UV light to some extent, so that melanin granules inside hair fibers show less sensitivity to UV light than they do when exposed in cross sections. However, phenomelanin is degraded due to its quite high UV sensitivity, regardless of any attenuation effects. Hair in which eumelanin is predominant has low sensitivity to UV light, and is not lightened by UV light alone during the short irradiation periods used in this experiment. Conversely, hair in which pheomelanin is predominant has high UV sensitivity and is lightened by it. Controversy regarding the photosensitivity of pheomelanin and eumelanin has lasted for some decades. Some researchers have argued that pheomelanin is more photolabile than eumelanin (11-13) other researchers have offered a contrary view (14). One of the reasons considered for this inconsistency is the state of the melanin granules that they investigated. When we study isolated or synthetic melanin, we see the photosensitivity of directly irradiated melanin. On the other hand, when studying the lightening behavior of hair fiber, especially regarding UV irradiation, we see the photosensitivity of melanin gran­ ules that were subject to light attenuation through absorption by hair protein. It follows that the sensitivity in this case is evaluated at a lower-than-real level. Actually, the researchers who argued that pheomelanin is more UV-labile than eumelanin performed their study mainly by using isolated and synthesized melanin (11-13 ), while other