j. Soc. Cosmet. Chem., 38, 99-107 (March/April 1987) Reduction of hair in the presence of exogenous disulfide LUDWIG SALCE, JOSEPH J. CINCOTTA, STEPHEN BARROW, ARNOLD RUBINSTEIN, and ERNEST J. KLEMM, Zotos International, Inc., Darien, CT 06820. Received January 7, 1986. Presented at the SCC Annual Scientific Meeting, New York, December 6, 1985. Synopsis Reduction studies on hair tresses were performed with commercially available ammonium thioglycolate and glyceryl monothioglycolate based perm lotions. Products formulated with exogenous disulfide were com- pared with those without added disulfide. Ratios of perming lotion to fiber weight were varied as were other experimental conditions. Reducing experiments were also performed on fiber bundles with am- monium thioglycolate solutions containing dithiodiglycolic acid at concentrations ranging up to 1.0 N. Quantitative results indicate that exogenous disulfide decreases the rate as well as limits the extent of hair fiber reduction. This effect is most marked under immersion conditions. Immersion experiments also show the rate of reduction to be inversely related to the concentration of added disulfide. While the effect is diminished with lower perm lotion-to-hair ratios, corresponding to practical waving conditions, this effect is still analytically evident. Thus the potential for over processing is reduced when exogenous disulfide is formulated into perming lotions. Both ammonium thioglycolate and glyceryl monothioglycolate based perms, containing added disulfide, behave in a similar manner. The effect of exogenous disulfide in permanent-waving lotions appears to be consistent with the equilib- rium nature of the keratin-mercaptan reaction. Excess lotion with exogenous disulfide produces a mass-ac- tion effect that moves the reaction to lower levels of keratin cystine reduction in the fiber. INTRODUCTION Approximately thirty years ago several patents were issued (1-3) describing advantages of waving hair with an aqueous mixture of a water-soluble mercaptan containing a water-soluble disulfide, over a pH range of 8.5 to 10. Formulations outlined in these patents were referred to as "effectively waving hair without imparting undesirable damage thereto." In addition, these perming lotions reportedly allowed greater flexi- bility in processing time while minimizing the possibility of overprocessing which is responsible for brittle, porous, dry, and unmanageable hair fibers. A more recent and novel utilization of disulfide for protecting hair during perming has been described in a patent issued in 1981 (4). This patent claims a "wrapping" composition, containing disulfide, that can be used to permanent wave "a head of hair having fibers of vastly diverse conditions intermixed throughout the head of hair." Although many commercially available waving lotions have utilized these concepts, 99

100 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS there is little quantitative chemical evidence appearing in the scientific literature that supports the phenomena reported in the patents mentioned above. This paper provides analytical data on the rate and extent of the reaction of hair fibers with mercaptan waving solutions formulated with and without added disulfide. Protective action of exogenous disulfide can best be explained if one considers keratin reduction proceeding through a two-step equilibrium reaction, often cited in the litera- ture (5), and as indicated in Equations I and II. I K-SS-K + RSH • K-SS-R + KSH II K-SS-R + RSH •---R-SS-R + KSH Overall the reaction can be summarized by Equation III, III K-SS-K + 2RSH •,• R-SS-R + 2 KSH and the equilibrium constant can be expressed by: (R-SS-R) (KSH) 2 K= (K-SS-K) (RSH) 2 Certainly, this is an oversimplification of the complex chemical interactions occurring in a system constantly changing from hydrophobic to hydrophilic, during keratin re- duction. That is, when the hydrophobic disulfide is reduced, a more hydrophilic sulf- hydryl group is formed. The latter is capable of ionization, especially under alkaline conditions. Rates of diffusion, complex heterogenous reactions, and true equilibria are ignored. However, as we shall see later in this paper, most of the data will be compara- tive in nature (i.e., thiol perming lotions of approximately similar concentrations with and without dithio compounds) and, therefore, any errors caused by this simplified approach should remain essentially constant throughout. Allowing for these assumptions, the Le Chateljer-Brown principle, at equilibrium, would predict that with exogenous disulfide (R-SS-R) the equilibrium reaction shown above would be displaced to the left so as to effectively decrease the formation of re- duced "keratin (KSH)." We have attempted to determine if addition of exogenous disulfide does indeed decrease reduction of keratin disulfide during hair waving. Several different experimental conditions were explored and the results obtained are presented. METHOD AND EQUIPMENT Virgin hair from a single donor, obtained from R. Parrino Hair Goods, Commack, New York, was used throughout this study. Load extensions were made on an Instron Model 1122 tensile tester interfaced with a Microcon II. Reduced hair strands were reacted with sodium iodoacetate and hydrolyzed by a modification described in the literature (6). The hydrolysis procedure used during this study differed from that ap- pearing in the literature in that an 18-hour atmospheric reflux, in 6 N HC1, was substituted for a sealed-glass-tube acid hydrolysis. Amino acid analyses of hair keratin hydrolysates were run on a Beckman Amino Acid Analyzer, Model ! 18CL, interfaced with a Perkin Elmer data station Model 3600. The methodology employed was recom- mended by Beckman in their application notes.