50 �� 40 CU·- Ill 0 .c 30 u • cu ..EJ 20 ._ en m E ... _ 10 c:C 0 3.2 2006 TRI/PRINCETON CONFERENCE 4.3 5.3 7.2 pH Value COCH By water Arg@ • coo- pH 6 By buffer (pH 3.5) 353 Figure 6. Recovery of Arg from hair. Arg treatment: 30 minutes immersion, 20 seconds rinse, 25 ° C. Recovery: 30 minutes immersion, 25 ° C. 25 cu- 20 ■= a:::-� J!I Ill a...l;= 15 ::::, ..EJ 10 c:C en oE a..- 5 0 1 2 3 4 5 6 pH Value PCA PCA@ 7 8 Figure 7. Uptake of PCA: pH dependence. PCA treatment: 5 wt%, 30 minutes immersion, 25 ° C. Re- covery: 30 minutes immersion, 25 ° C. in cosmetic preparations. Some beneficial effects found on bleached/dyed hair are de- scribed in this section. Damage care by various amino acids. Bleaching hair decreases hydrophobicity of hair fiber (5). Figure 9 shows surface hydrophobicity of bleached hair treated with hair condition- ers. The average contact angle for natural hair was 100° and four-time bleach treatment brought it down to 65°. By application of a simple model hair conditioner of monoalkyl trimmonium chloride, the contact angle increased slightly. With 1.5 wt% of 1-alanine addition, the contact angle increased significantly to the similar value to that of dialykyl trimmonium. Decrease in tensile strength of dyed hair fibers is not clear when it is measured in the dry state, but the effects of oxidization are clear when measurements are made in water (8,9). Figure 10 shows tensile strength of bleached hair measured in water. Tensile strength decreased by four-time bleach treatment, and significant increase was observed

354 JOURNAL OF COSMETIC SCIENCE 4.0 N=3, mean± S.D. CD 'i:" 3.0 � ·- J!I .. CL"T 2.0 ::::, .ea cm a.- 1.0 0.0 PCA-Arg PCA-Na Figure 8. Uptake of PCA: the effect of counter ion. PCA treatment: 5 wt%, 30 minutes immersion, 25 ° C. Recovery: 30 minutes immersion, 25 ° C. [: C J! C 0 u § 41 .c ... � "iii 110 100 90 80 70 60 50 N=20 �i I ii♦•+•-,l·•-1** : o111111 *: p0.05, **: p0.01 '1111111 Bleached --'------------------'-----------=----' Dunnett's test, control= STAG Natural Bleach STAC STAC +Ala DSDAC Figure 9. Improvement of surface hydrophobicity. 5D-�--------------------------� 10- .., __________ Bleached Q-'----�---------------------------' Natural Control Phe His Ala lie Arg Glu Figure 10. Improvement of tensile strength. ••: p0.01 Dunnett's test by application of phenylalanine or histidine. In fact, this increase is attributed to the increase of hair fiber diameter with the tensile strength per area being unchanged. These amino acids are probably diffused into hair fiber and interact with protein to influence the structure. IMPROVEMENT OF COLOR RETENTION BY SODIUM PCA Salts of PCA are highly hygroscopic. This property is expected to contribute to retention of not only water but also other water-soluble molecules in hair fibers, such as dye molecules.