360 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS FI(%) 100- 80' 40' 20' (a) Unbleached o o 1•o 20 40 60 8'0 100' 80' 40' (b) 6% H202, 4 hours o o 2'0 4'0 6'o 8'0 1•o 100' 80' 20' (c) Bleach creme, 30 minutes 0 0 1•0 2 '0 4 0 6 '0 8 '0 DISTANCE ( pm ) Figure 9. Micrographs of unbleached and bleached hair fiber cross sections dyed 5.5 h with 0.1% uranin and corresponding cross-sectional fluorescence intensity scans.

EVALUATION OF HAIR DAMAGE 361 Table IV Cysteic Acid Content of Bleached Human Hair Cysteic acid Dissolved fiber (Ixmoles/g) (mol %) (%) Untreated n.d. * n.d. * 70 6% H202 2 min X 10 114 2.6 52 30 min 148 2.3 78 1 hour 192 3.4 67 4 hours 302 5.2 70 Bleach creme 211 3.7 68 * n.d., Not discernible less than 40 p. moles/g cannot be detected by this method. 2. Permed hair. The mechanical properties of unbleached and moderately bleached hair (four hour, 6% H202) were reduced by the first and by each of two successive perm treatments (Table VI). Overall, the effects on the bleached hair sample were similar to those on the unbleached hair through each successive perming cycle. The only difference in the treatments was that the concentration of the thioglycolate solution was halved for bleached hair in accordance with the usual salon practice. Although these surface properties were only slightly affected by the perming process, the bulk fiber properties were dramatically decreased by the perm treatments. In Figure 10, typical Instron load-extension curves are shown for unbleached and bleached hair. These are generalized curves with specific mechanical properties seen in Table VI. The size and area of the curves decrease with each successive perm treatment. The overall mechanical properties decrease accordingly. For bleached hair with repeated perm treatments, the loss of mechanical properties after one perm is even more dramatic, and by the third perm, the load-extension curve is greatly diminished. The loss of bulk properties is obviously not reflected in surface wettability, which is a reflection of the fact that the properties of the cuticle have little effect on the bulk properties of the hair fiber. In general, the mechanical properties of both unbleached and bleached hair were reduced by repeated perm treatments. The major difference between unbleached and bleached hair was that the first perm treatment had a more profound effect on bleached hair. In fact, the level of first perm damage on bleached hair was similar by some measures to that produced by three perm treatments on unbleached hair. Table V Wet Mechanical Properties of Bleached Hair Work to Work to Bleach Modulus Yield stress extend 20% Breaking stress break treatment (GN/m 2) (GN/m 2 X 10 -2) (MJ/m 2 x 10-•) (GN/m 2 X 10-•) (MJ/m 2) Untreated 2.8 -+ 0.23* 6.7 +- 0.76 4.4 +- 0.71 3.3 +- 0.31 2.6 +- 0.31 6% H202 2' X 10 2.6 +- 0.28 5.7 +- 0.79 3.8 +- 0.79 3.0 -+ 0.32 2.3 +- 0.30 4 hrs 2.5 +- 0.23 4.9 +- 0.69 2.7 +- 0.27 2.8 +- 0.32 2.2 +- 0.32 Bleach creme 2.1 + 0.02 -- 2.8 -+ 0.32 2.1 + 0.23 1.7 + 0.30 * 95% Confidence limits.