EFFECTS OF MERCAPTANS ON HAIR 533 other reduced hairs. It appears that the distance between proteins is extended due to the cleavage of much of the cystine in TG-reduced hair. Otherwise it was probably due to the effect of the cleavage of cystine existing in a different environment (18). In permed hair, the relationship between the extent of degradation and water retention is shown in Figure 6. It was found that there was a linear correlation between the extent of degradation and water retention. Notice that the water retention and protease degrad- ability increased with repetitive treatment. In hair permed both three and six times, the degradability and water retention of hair increased in the following order: CYS-treated hair CA-treated hair TG-treated hair. SCANNING ELECTRON MICROSCOPY (SEM) Figure 7 shows typical surface morphology of hair permed three times after protease treatment. The lateral area of TG-permed hair (a) shows that the major part of the cuticle layers was degraded. The degradation was found to affect the inner part of the hair due to a pleated, irregular, and porous cross-section in contrast to other hairs. Figure 5. Correlation between the degradation extent and the water retention of hair reduced with TG, CA, and CYS. The reduction time of the reduced hair is 3, 5, 10, and 15 min. The hair source is the same as in Figure 4. Figure 6. Correlation between the degradation extent and the water retention of hair repetitively permed with TG, CA, and CYS. Numbers 3 and 6 correspond to the number of repetitive times. The hair source is the same as in Figure 4.

JOURNAL OF COSMETIC SCIENCE 534 The lateral areas of CA-permed hair (b) and CYS-permed hair (c) exhibited relatively clear cuticle edges, suggesting that the protease degradation of the cuticle layer is not very much advanced. The degradation of CA-permed hair was a little greater than that of CYS-permed hair. Since the cross sections of CA- and CYS-permed hair were relatively plainer than that of TG-permed hair, the degradation was found to be not very much advanced in the inner part of the hair. As a result, it was found that the surface morphol- ogy of hair after protease treatment refl ects its degradability. CONCLUSIONS The protease degradability of reduced hair and permed hair was related to the reduction power of the mercaptans used on the hair. The degradability increased in the following order: CYS-treated hair CA-treated hair TG-treated hair. In reduced hair, it appears that accessibility may be increased due to the cleavage of di- sulfi de bonds. Therefore, reduced hair became swellable and enzymatic attack was found to increase. As a result, the degradability of reduced hair progresses further. In permed hair, though the cleavage of disulfi de bonds was remarkably small even with repetitive treatment, accessibility is relatively high. Thus the swellability and degradability of re- petitively permed hair appears to progress. Protease degradation is a useful method for evaluating damaged permanent-waved hair. The method is simple, and hair damage can be assessed both visually and through gravimetric analysis. ACKNOWLEDGMENTS We thank Dr. T. J. Lin for his valuable guidance in this research work. Mr. Koji Takano is gratefully acknowledged for his assistance with the SEM procedure. Finally, we would like to express our appreciation to Mr. M. Okano, Mr. T. Yoshida, and Mrs. A. Karasawa, for their discussions and guidance. REFERENCES (1) C. Zviak and A. Sabbagh, “The Science of Hair Care,” in Permanent Waving and Hair Straightening, B. Claude and W. John, Eds. (CRC Press, Boca Raton, FL, 2005), pp. 201–228. Figure 7. SEM photographs of hair after pronase E treatment. (a) TG-permed hair, 3 times. (b) CA-permed hair, 3 times. (c) CYS-permed hair, 3 times. The extent of protease degradation is (a) 19.2%, (b) 16.9%, and (c) 16.2%.