BLEACHING OF HAIR 189 which is almost undistinguishable from that obtained from hydrogen peroxide-bleached melanin (6). The difference in photo-bleaching response between the eu- and pheomelanin is doubt- lessly associated with their different chemical make-up. It is not known whether this difference is expressed at the primary level, which involves presumptive production of superoxide anion, or at the secondary level, the resistance to oxidation, which deter- mines the bleaching propensity. Recent publications (9, 10) on the photo-induced ox- ygen consumption in melanin systems suggest little difference between eu- and pheo- melanins, thus implying that superoxide formation might be similar for both pig- ments. Therefore, we evaluated the oxidative stability of both pigments by carrying out bleaching experiments with the red and brown hair. Our findings (Figures 9 and 10) suggest that eumelanin is more labile than pheomelanin (as measured by color changes) to oxidative degradation by H20 2. These results parallel those observed for photo- bleaching, although the magnitude of the difference (Figure 11) is greater in this case, probably being related to more extensive solubilization of the pigment that occurs in bleaching. This similarity in the pattern of response also points to a possibility of a common mechanism underlying both photo- and chemical bleaching. On the basis of data presented here, it would appear that the benzothiazine units of pheomelanin are 35 30 25 20 15 lO 5 i i i I i i • 400 500 600 700 Wavelength (nm) Figure 10. Reflectance spectra of brown hair be•re (¸) and a•er (O) bleaching with H202.

190 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS more resistant to oxidation than the indolic residues of eumelanin. The fact of the matter is, however, that we do not know for certain what precisely are the structures of these pigments, and the discussion of their relative stability would be highly specula- tive. The appearance as well as the reflectance curves of the brown hair after bleaching points to a significant increase in redness. In fact, one of the most common observations frequently made during bleaching of hair--particularly highly pigmented hair--is the development of red tones. On the basis of the results presented here, we conclude that the primary reason for this "red" shift is the breakdown and the solubilization of the pigment particles. Both of the above significantly depress the light-scattering contribu- tion of the individual and aggregate melanosomes, intensifying at the same time the contribution of the pigment light absorption characteristic. Our data on the photoreactivity of the pheo- and eumelanins may have a bearing on the understanding of the photoprotective role of the pigments. In terms of the sunscreen characteristics, both melanins are alike (they display similar absorbance spectra in the region of interest), they are both effective as oxygen detoxifiers, and in terms of degra- dation, the pheomelanin is less photolabile. It seems to us that the suscept!bility of 250 200 150 100 50 I I I i I i i 400 500 600 700 Wavelength (nm) F•urell. Changeinreflectanceofbrown(O) andred(O)haira•erbleachingwith H202.