BLEACHING HUMAN HAIR 345 Small quantities of these same two pyrolic acids (and other pyrolic acids) have been isolated from the oxidation of sepiomelanin with per- manganate or with hydrogen peroxide in acetic acid (39, 40). This latter reaction most likely involves attack by peracetic acid on melanin rather than attack by the hydroperoxide anion or the hydrogen peroxide mole- cule, as probably occurs in hair bleaching (41). The isolation of pyrolic acids from the oxidation of melanin is con- sistent with the previous suggestion that the indole quinone grouping is a major repeating structural unit. The low yields of isolated pyrolic acids (generally less than 1%) may be explained on the basis that these fragments are themselves sensitive to oxidation however, a second ex- planation suggests a multiplicity of sites in the pigment macromolecules that are susceptible to attack by oxidizing agents producing many unre- covered fragments. In more pertinent experiments, Wolfram et al. (10) have studied the reaction of alkaline hydrogen peroxide with melanin granules isolated from human hair. These authors suggest an initial solubilization followed by decolorization. Several products derived from melanoprotein were isolated from these reactions, including protein- aceous species rich in the dibasic amino acids, and several other products ranging up to 15,000 in molecular weight. Further identification of these fragments should provide interesting information concerning the struc- ture of melanin and the mechanism of its oxidative degradation during bleaching. The pigments in red hair are structurally different from the brown- black melanins (42). The chromophoric unit (Fig. 6) of the red pigments is of low molecular weight (560) as compared to the polymeric melanins. However, the aromatic rings of this structure are of high electron density and, as a consequence, should be sensitive to attack by oxidizing agents. One may conclude from the current knowledge of the structures of the melanins and the trichosiderins that they are similar enough to be sensi- tive to oxidation, yet dissimilar enough to react through different mecha- nistic schemes during oxidative deg•'adation. A more complete under- standing awaits further study. OH H OH __ I C02H • HO- C--CH •' NH 2 CH 2 -- •H-NH 2 C02H Figure 6. Structurc of the pigment trichosiderin suggested by Prota

346 .JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS SUMMARY A review of hair bleaching describing reactions of bleach agents with the proteins of human hair and with hair pigments is presented. Support for diffusion-controlled oxidative cleavage of the disulfide bond during bleaching is described. Evidence for oxidation of cystyl residues in hair through S--S fission instead of C--S fission is presented and possible end products of the oxidation reaction are described. The low yields of prod- ucts (pyrolie acids) isolated from the oxidation of melanins suggest that these species are themselves sensitive to oxidation, and/or that several different functional groups in the pigment macromolecule may be suscep- tible to attack by oxidizing agent. ACKNOWLEDGMENT The author would like to acknowledge Dr. M. L. Douglass for care- fully reading this manuscript and for helpful suggestions. (Received December 21, 1970) REFERENCES (1) Maclaren, J. A., Leach, S. J., and Swan, J. M., A study of some problems in protein chemistry using new (non-hydrolytic) methods for the determination of thiol and disul- fide, J. Text. Inst., 51, T 665-7 (1960). (2) Maclaren, J. A., Savige, W. E., and Sweetman, B. J., Disulfide monoxide groups in oxi- dized proteins, Aust. J. Chem., 18, 1655-65 (1965). (3) Robbins, C., Infrared analysis of oxidized keratins, Text. Res. J., 37, 811-3 (1967). (4) Alter, H., and Bit-Alkhas, M., Infrared analysis of oxidized keratin, Ibid., 39, 479-81 (1969). (5) Nachtigal, J., and Robbins, C., Intermediate oxidation products of cystine in oxidized hair, Ibid., 40, 454-7 (1970). (6) Zahn, H., Chemical processes in the bleaching of wool and human hair with hydrogen peroxide and peroxy acids, ]. Soc. Cosmet. Chem., 17, 687-701 (1966). (7) Robbins, C., and Kelly, C., Amino acid analysis of cosmetically altered hair, Ibid., 20, 555-64 (1969). (8) Nicolaus, R. A., Comments on Howard S. Mason's Paper "The Structure of Melanin," in Montagna, W., and Hu, F., Advances in Biology of Shin, The Pigmentary Sy,•tem, Vol. 8, Perga•non Press, New York, 1966, pp. 313-4. (9) Mason, H. S., The Structure of Melanin, in Montagna, W., and Hu, F., Advances in Biology o/Shin, The Pigmentary System, Vol. 8, Pergamon Press, 1966, pp. 293-312, and references therein. (10) Wolfram, L., Hall, K., and Hui, I., The mechanism of hair bleaching. J. Soc. Cosmet. Chem., 21,875-900 (1970). (11) Flesch, P., Chemical studies of the iron pigments of red hair and feathers, Ibid., 19, 675-81 (1968). (12) Prota, G., Schevillo, G., and Nicolaus, R. A., On the structure of trichosi(lerins, Rend. Accad. Sci. Fis. Mat., Naples. 35, 1-4 (May, 1968).