EFFECTS OF MERCAPTANS ON HAIR 531 process, cystine is regenerated and the protein structure becomes more closely packed. For this reason, it appears that the protease attack is less effective, and so the permed hairs showed a small difference in degradability between different mercaptan treatments. Yet these results also indicate that a structural change also occurs with permanent waving treatment that cannot be reversed by oxidation treatment. EFFECT OF CYSTINE CONTENT OF HAIR In order to compare the cystine content of hair with different mercaptan treatments, we measured cystine reduction as a function of reduction time. As shown in Figure 3, the cystine reduction no longer increased after 30 min of reduction in each mercaptan treat- ment. This fi nding indicates that the reduction in each mercaptan treatment is almost fi nished at around 30 min, at which time the penetration of mercaptans may be fi nished (3,4). Furthermore, in the entire reduction time, the cystine reduction of CYS-treated hair was smallest for all hairs, that of CA-treated hair was much higher, and that of TG- treated hair was greatest. Especially in the case of TG-reduced hair, about 90% of cystine was cleaved after about 30 min of reduction. Figure 2. Correlation between the degradation extent and the reduction time of permed hair. The reduction time of the permed hair is 5, 10, 15, 20, and 30 min. The oxidation time was fi xed at 15 min. Figure 3. The time course of cystine reduction of hair with different mercaptans. Cystine reduction % (paren- theses show the reduction time): TG reduction: 0(0), 13.1(3), 21.5(5), 44.7(10), 65.0(15), 80.4(20), 85.0(25), 89.0(30), 91(40). CA reduction: 10.3(3), 15.8(5), 33.7(10), 39.0(15), 43.0(20), 53.0(25), 54.3(30), 55.0(40). CYS reduction: 4.5(3), 8.9(5), 15.8(10), 18.0(15), 20.6(20), 21.0(25), 22.0(30), 23.4(40).

JOURNAL OF COSMETIC SCIENCE 532 Gumprecht et al. (16) reported much lower cystine reduction than shown in our data, on the order of only 20% in spite of similar conditions. The difference in cystine reduction is believed to be due to the solution-to-hair ratio. It has been known that in cystine re- duction, larger concentrations of mercaptan than cystine in hair should drive a reaction to completion (17). Gumprecht et al. used a simulated actual hair-waving method they used a solution-to-hair ratio of about 1:1, while we used a ratio of 10:1. This is the reason why our data show the much higher cystine reduction. Cystine reduction is considered to be one of the most important factors in protease deg- radation. We compared the relationship between the extent of degradation and cystine reduction for the reduced hair and permed hair (Figure 4). The reduced hair was used with the different reduction time described above. The permed hair was used with re- petitive treatment, because the cystine reduction of hair permed only once was remark- ably low. In the reduced hair, all points were plotted on the same curvature in spite of different mercaptan reductions. The degradation appears to be affected by cystine con- tent. In permed hair, it was found that there was a correlation between the extent of degradation and cystine reduction. The cystine reduction of permed hair was remarkably small even with repetitive treatment. This fi nding indicates that the extent of degrada- tion of permed hair is nearly unaffected by its cystine content. EFFECT OF WATER RETENTION OF HAIR Protease degradation of hair occurs in aqueous media. Therefore, protease degradation is considered to be affected by water retention of hair (14). We measured the water retention of reduced and permed hair. The relationship between the extent of degradation and wa- ter retention of the reduced hair is shown in Figure 5. In CA- and CYS-reduced hair, the data were plotted in the same linear relationship, and in TG-reduced hair, the data were plotted on a curve. The behavior shows that the TG-reduced hair is more swellable than Figure 4. Correlation between degradation extent and percentage of cystine reduction in reduced and permed hair. The reduction time in reduced hair is 5, 10, 15, 20, and 30 min. The repetitive time of permed hair is 1, 3, and 5 times. The degradation extent (%) of reduced hair (parentheses show the reduction time): TG-reduced hair: 8.4(0), 16.0(5), 20.0(10), 23.5(15), 27.0(20), 32.4(30). CA- reduced hair: 14.5(5), 17.1(10), 19.8(15), 21.2(30). CYS-reduced hair: 12.6(5), 13.5(10), 14.7(15), 15.6(30). The degradation extent (%) of permed hair (parentheses show the repetitive time): TG-permed hair: 8.4(0), 14.0(1), 19.2(3), 27.5(5). CA-permed hair: 13.5(1), 16.9(3), 18.5(5). CYS-permed hair: 13.0(1), 16.2(3), 17.3(5).