464 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1.0 0.8 0.6 0.4 0.2 0.0 I -•! \*- Product A -i • pH12.5 \ Product B - •xX'pH 12.0 2 4 6 8 I I I I 10 12 14 16 Time (minutes) Figure 2. Stress decay of human leg hair by commercial depilatories. after treatment for various times with these two products. The products were applied to circular patches of the subject's legs, controlling amount/unit area, after clipping the hair to a uniform V4" length. Hair was removed with firm strokes of a damp washcloth. Percent removal was estimated by two judges. At both 4 and 6 minutes, product B had removed more hair than product A. The T95 % measurement correctly predicted the order of effectiveness of these two products and gave a reasonable approximation of the time for complete removal of hair. REPRODUCIBILITY OF THE T95 % MEASUREMENT The reproducibility of T95 % for head hair treated with either a commercial depilatory cream or 0.5M thioglycolate (TGA) solutions at pH 11.5 is shown in Table II. Means and standard deviations for 22 and 14 runs, respectively, are shown. Data in Table II are for different hairs from the same source. Since only a short section of hair (1.5-2.5 Table I Percent Removal of Hair by Commercial Depilatories vs. Treatment Time Product A Product B Time Right Leg Left Leg Right Leg Left Leg 4 min. 25% 30% 40% 75% 6 min. 90% 90% 100% 100% 10 min. 100% 100% 100% 100%

SINGLE FIBER DEPILATORY STUDIES 465 Table II Reproducibility of T95 • Measurement Average Standard System T95 % Deviation n Cream B 5.9 min. 1.2 min. 22 0.5 M TGA, pH 11.5 8.1 min. 1.2 min. 14 cm) is needed for the measurement, many measurements can be made using the same hair. When this is done, results of duplicate treatments generally agree to within 1 minute. The hair used in this work was approximately 12 inches long 2 inches near the tip end were trimmed off prior to cutting sections for analysis. No consistent root-to-tip variation in reduction rate was seen. One might expect abrasion and weathering of the hair to lead to higher reduction rates however, we did not observe this, and Yablonski and Williams (1) reported that deliberate abrasion of hair with a spatula did not in- crease the rate of swelling in depilatory solutions. In subsequent figures shown in this report, all curves in a given figure are from different sections of the same hair. T95 % values in the tables to follow were obtained by averaging two runs, and all values compared in a given table are from runs on the same two hairs. EFFECT OF OXIDATIVE PRETREATMENT ON REDUCTION RATE Oxidative pretreatments may increase rates of subsequent reactions by increasing the rate of diffusion of reactants into the hair. Figure 3 shows effects of 30-minute pretreat- ments with buffer or 10% hydrogen peroxide at both pH 7 or 11 on subsequent SFTK results with TGA solutions at pH 10.5. Pretreatment with hydrogen peroxide at pH 11 reduced T95 % from eight to three minutes. The increase in rate was caused by oxidative • •.'..•..•, x.•..-10% H202, pH 7 0.2 - \ •'"".',, 'x %'• 10% H202, pH 11 o.o "--'. ............ , ........ 0 2 4 6 8 10 12 14 16 Time (minutes) Figure 3. Effects of peroxide treatment on subsequent stress decay in 0.5 M TGA at pH 10.5.