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J. Soc. Cosmet. Chem., 47, 213-227 (July/August 1996) Reduction of human hair by cysteamine and ammonium thioglycolate: A correlation of amino acid analysis and single-fiber tensile kinetic data MELISSA A. MANUSZAK, EDWARD T. BORISH, and R. RANDALL WICKETT, College of Pharmacy, University of Cincinnati, 3223 Eden Avenue, Cincinnati, OH 45267 (M.A.M., R.R.W. ), and L & F Products, 1 Phillips Parkway, Montvale, NJ 07645 (E.T.B.). Accepted for publication July 31, •996. Presented at the Annual Scientific Seminar of the Society of Cosmetic Chemists, May 4-5, 1995. Synopsis A study was conducted to determine the effects of reduction by cysteamine and ammonium thioglycolate (ATG) on the physical and chemical properties of human air. The methods utilized were amino acid analysis with ortho-phthaldehyde derivatization (OPA) and a modification of the single~fiber tensile kinetics (SFTK) method. Virgin, medium brown hair from a single source (DeMeo Brothers) was used for all of the experiments. Stress relaxation of hair fibers was monitored to determine the rate of reduction of stress- supporting disulfide bonds by cysteamine and ATG. Levels of cystine and cysteine were monitored by amino acid analysis to determine the rate of reduction of disulfide bonds in the whole fiber. The results of this study indicated that the rate of reduction of both stress-supporting and whole-fiber disulfide bonds by ammonium thioglycolate was faster than the rate of reduction by cysteamine. The kinetic results obtained by stress relaxation were found to agree with the results from amino acid analysis. INTRODUCTION The kinetic behavior and mechanisms of action of various mercaptans have been inves- tigated by monitoring stress-relaxation and stress-strain behavior of hair fibers (1-3). The results of these studies indicate that dramatic effects may result when parameters such as temperature, pH, or concentration of the reducing agents are varied. The mercaptans, which are used to produce a permanent wave, attack the disulfide bonds in the hair and cleave these bonds so that they may be reformed in a new configuration. This reduction of disulfide bonds has been shown to proceed through two displacement Current addresses: Melissa Manuszak, Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803 Edward T. Borish, Zotos Corporation, 100 Tokeneke Road, Darien, CT 06820. 213