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.

EXOGENOUS DISULFIDE IN HAIR REDUCTION 105 experiments performed in the presence of excess lotion. Quantitatively, however, results obtained with limited lotion (10.0 ml) differ in that keratin disulfide reduction is substantially lower and maximum equilibrium cleavage is obtained sooner. With am- monium thioglycolate based lotions, maximum cleavage is obtained in only five minutes, and with GMT-based lotions, after twenty minutes. These experimental conditions are referred to as a "closed system" since any disulfide formed during reduction cannot migrate into excess surrounding liquid as is possible in the immersion studies. Hence, there is a constant "build up" of disulfide in the hair fiber, with a concomitant decrease in thiol concentration, as reduction proceeds. If the equilibrium situation in the equations given earlier apply, one would expect from mass-action effects that the presence of exogenous disulfide would result in less keratin reduction. LIMITED LOTION--ROD IMPLANT METHOD Attempting to replicate actual salon perming conditions, in which the lotion-to-hair ratio is lower than in the limited lotion rod method just described, 2.0 g hair strands were water-wrapped onto 6.35-mm rods and placed ("implanted") onto the head of models having their hair permed in a test salon (See Table III for experimental condi- tions). Periodically the "implants" were removed and reacted with iodoacetate to form the carboxymethyl derivatives of the reduced cystine (cysteine). Amino acid analyses of treated strands were used to calculate percent reduction of the keratin cystine. It should be noted that in one experiment perm solution A (0.8 N-RSH, pH-9.2) was lotion- Table III Cysteine Cleavage in Hair Treated With Mercaptan or Mercaptan-Disulfide Mixtures for Various Lengths of Time (Limited lotion--rod implant method) Processing time Cystine cleaved Perm Type (min) (%) A NH4-T 5 13.8 (26.8) • (0.8 N, pH-9.3) 20 27.3 (48.4) • B NH4 T (1.0 N, pH-9.2) 5 10.8 + 20 21.3 DTDGA (0.25 N) C 2 GMT 5 19.4 (1.18 N, pH-6.7) 20 29.3 @ 53øc D 3 GMT (1.29 N, pH 7.6) 5 1.9 + 20 22.7 DGDTDG (0.25 N) @ 45øC NH4-T, Ammonium thioglycolate. DTDGA, Dithiodiglycolic acid. GMT, Glyceryl monothioglycolate. DGDTDG, Diglyceryl dithiodiglycolate. Lotion-wrapped. Processed under hair dryer at 53øC. Exothermic perm, initial temperature 45øC.