EXOGENOUS DISULFIDE IN HAIR REDUCTION 103 Table I Cysteine Cleavage in Hair Treated With Mercaptan or Mercaptan-Disulfide Mixtures for Various Lengths of Time (Excess lotion-- immersion methodS) Processing time Cystine cleaved Perm Type (min) (%) A NH4-T 5 76.5 (0.8 N, pH-9.3) 20 86.1 30 90.1 B NH4T (1.0 N, pH-9.2) 5 40.8 + 20 56.3 DTDGA (0.25 N) 30 53.8 40 54.3 C GMT 5 14.0 (1.18 N, pH-6.7) 20 38.4 30 58.4 40 71.9 GMT (1.29 N, pH-7.6) 5 9.3 + 20 21.8 DGDTDG (0.25 N) 40 31.8 NH4-T, Ammonium thioglycolate. DTDGA, Dithiodiglycolic acid. GMT, Glyceryl monothioglycolate. DGDTDG, Diglyceryl dithiodiglycolate. All processed at room temperature. mately twenty minutes and remains close to this value even after forty minutes of immersion. On the other hand, perm lotion A (0.8 N-RSH, pH-9.3), containing no exogenous dithiodiglycolate, continues to reduce hair and after only thirty minutes 90% of the theoretical cystine disulfide bonds are reduced. Hence, the weaker perm lotion A (0.8 N-RSH), containing no dithio compound, reduces more keratin cystine than perm solution B of higher thiol concentration (1.0 N-RSH) containing diam- monium dithiodiglycolate. In a similar manner, reduction of hair fibers with a glyceryl monothioglycolate based perm lotion D (1.29 N-RSH, pH-7.6) containing diglyceryl dithiodiglycolate reduces keratin at a much slower rate than the dithio-free perm solution C (1.18 N-RSH, pH 6.7), even though perm solution C is at a lower pH (pH-6.7) and lower thiol content than perm lotion D (pH-7.6). Differences in lotion concentrations are due to the fact that the perming solutions em- ployed in this study were commercially available and were used without modification. Reduction of hair fibers in a large excess of perming lotion by immersion will be re- ferred to as an "open system" since both the mercaptan and disulfide molecules are free to diffuse into and out of the hair fiber and migrate into a solution containing a large excess of these water-soluble chemical species. Although these are not conditions under which hair is permed in a salon, the moderating effect of disulfide compounds on the rate of keratin reduction by water-soluble mercaptans is clearly evident.

104 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS LIMITED LOTION--ROD METHOD In an effort to approach a realistic ratio of hair fiber to reducing lotion, a second series of studies was performed. In these experiments, the hair strands were water wrapped onto 6.35-mm perming rods and then saturated with 10 ml of waving lotion at temperatures and conditions indicated in Table II. After processing for different time periods, the tresses were reacted with iodoacetate to convert any reduced keratin cystine (cysteine) to its carboxymethyl derivative. Results from these experiments are summarized in Table II. Ammonium dithiodiglycolate present in perm lotion B (1.0 N-RSH) limits cystine reduction to approximately 31%, while perm solution A (0.8 N-RSH), in the absence of added dithio compounds, permits reduction to proceed to an average of 42.5%. Again, higher percent reduction of perm solution A appears more impressive if one considers the fact that perm solution A is 0.8 N-RSH, while perm lotion B is 1.0 N-RSH. A similar trend is evident when a comparison of reduction values is made between GMT-based perm solutions such as C (1.18 N-RSH, pH-6.7) and D (1.29 N-RSH, pH-7.6). After forty minutes, perm lotion D, containing diglyceryl dithiodiglycolate, reduced only 25.6% of the fiber disulfide, while perm solution C reduced 39.4% of the cystine. Note that perm solution C, at the lower pH (pH-6.7) and without exogenous disulfide, is more reactive than perm lotion D having a higher pH (pH-7.6) and higher thiol content, but containing a dithio compound. These results are qualitatively similar to those obtained for the immersion perming Table II Cysteine Cleavage in Hair Treated With Mercaptan or Mercaptan-Disulfide Mixtures for Various Lengths of Time (Limited lotion--rod method) Processing time Cystine cleaved Perm Type (min) (%) A NH4-T 5 43.1 (0.8 N, pH-9.3) 10 42.5 20 41.7 B NH4 T (1.0 N, pH-9.2) 5 30.9 + 15 30.8 DTDGA (0.25 N) 20 31.6 C • GMT 5 15.1 (1.18 N, pH-6.7) 20 43.0 @53øC 40 39.4 D 2 GMT (1.29 N, pH-7.6) 5 6.9 + 20 25.0 DGDTDG (0.25 N) 40 25.6 @ 45øC NH4-T , Ammonium thioglycolate. DTDGA, Dithiodiglycolic acid. GMT, Glyceryl monothioglycolate. DGDTDG, Diglyceryl dithiodiglycolate. Processed under hair dryer at 53øC. Exothermic perm, initial temperature 45øC.