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J. $oc. Cosmet. Chem., 21, 875-900 (Dec. 9, 1970) The Mechanism of Hair Bleaching LESZEK J. WOLFRAM, Ph.D., K. HALL, B.Sc., and I. HUI, M.Sc.* Presented December 2, 1969, New York City Synopsis--The color of mammalian HAIRS is due mainly to the inclusion of discrete, darkly colored MELANIN granules in the keratinized cytoplasmic protein of the fiber-forming cells. During BLEACHING the melanin pigment undergoes irreversible physicochemical changes which result either in the toning down or complete elimination of the original fiber color. The modification of the fiber protein (KERATIN) attendant upon bleaching is largely confined to the oxidation of combined CYSTINE. The cysteic acid residues formed in this reaction cause a significant change in the distribution of electrostatic cross links. INTRODUCTION Peroxide bleaching of pigmented keratin fibers has been prac- ticed for many years, yet no published account of any comprehensive study of the kinetics or mechanism of the process is available. Litera- ture concerning the physicochemical changes in the pigment is prac- tically nonexistent that dealing with keratin modification attendant upon bleaching is relatively rich (1-15), but mainly devoted to general- ities, and often contradictory. This is not surprising in view of the fact that the various authors who have studied the bleaching process em- ployed widely differing conditions of treatment. As the aim of bleaching is to eliminate or tone down the natural hair color, the process is directly related to the structure and reactivity of the hair pigment. Two principal approaches to understanding the structure of melanin have been tried. The analytical approach has * Gillette Company Research Institute, 1413 Research Blvd., Rockville, Md. 20850. 875