368 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS to any other group of samples. This suggests the deposition of conditioner-surfactant complexes on the fiber surface, which release surface-active compounds during the wettability scan (13). Materials can accumulate on hair surfaces from a number of cosmetic applications and environmental sources for example, conditioning polymers are deposited from sham- poos and conditioner formulations. Previous studies at TRI on many different condi- tioning polymers have shown that most of the excess conditioner polymers rinse off in successive water immersions (14), although conditioner-surfactant complexes can lead to considerable buildup in multiple applications (15). The average values of work of adhesion provide additional information about changes on the hair surface. Figure 14 shows the work of adhesion for the grooming sequences on the highly oxidized hair sample. As shown above, bleaching destroys the hydrophobicity of the untreated fiber surface, rendering it quite hydrophilic. As seen for combing of these fibers, two of the combed samples, 4B 1 (combed only), and 4B3 (shampooed and combed), significantly lowered the work of adhesion of the bleached control sample (4BO). Combing appears to produce a less hydrophilic fiber surface, which suggests abrasive removal of hydrophilic layers. The sample that was shampooed, conditioned, and combed shows a work of adhesion value only slightly lower than that of the uncombed samples, suggesting less of an effect from combing due to the presence of the conditioner. Structural damage Dye diffusion. Chemical and structural modifications due to bleaching were found to W (mN/m) 11o lOO 90 80 70 ß ß 4BO 4B1 T 4B2 4B3 4B4 Treament Figure 14. Work of adhesion for grooming sequences on hair bleached four hours in H202.

EVALUATION OF HAIR DAMAGE 369 cause increases in the rates of diffusion of dyes into hair fibers in our previous work with uranin. However, cross-sectional fluorescence intensity profiles of groomed hair tagged with the fluorescent tracer showed similar diffusion patterns, indicating that subsequent grooming, for ten cycles or a total of 1,000 combing strokes, did not produce significant differences in diffusion rates for either the unbleached or the bleached samples. Mechanicalproperties. Abrasive damage experienced during grooming would be expected to be restricted to the fiber cuticle and possibly lead to its total loss. It has recently been demonstrated (16) that oxidative cuticle damage even under quite severe conditions does not appear to cause a reduction in tensile properties, which supports the hypothesis that the tensile properties of human hair are primarily those of the cortex. In evaluating the original bleached hair, we observed that the nonultimate mechanical properties seem to be more sensitive to oxidative damage than the properties obtained at fiber failure. If damage from grooming sequences is indeed mainly a surface abrasion effect, we would not expect to see significant changes in mechanical properties. On the other hand, the shampoo treatments and intermittent stretching from combing may lead to structural weakening, which could be reflected in both the ultimate and nonultimate mechanical properties. In general, the effects of grooming bleached hair were minor on the mechanical prop- erties of modulus, breaking stress, and work to failure, as seen in Table VIII. The incorporation of conditioner into the grooming process had an alleviating effect on whatever damage was encountered during grooming. Significant differences arose in the evaluation of 20% work and yield stress, however. Improvement in 20% work with the addition of conditioner was clear. In evaluating yield stress for unbleached and bleached hair, we found that shampooing and combing always was most damaging and that the incorporation of a conditioning step into the Table VIII Mechanical Properties of Groomed Hair Modulus Yield stress Treatment (GN/m 2) (GN/m 2 x 10- 2) Work to extend 20% Breaking stress Work to break (MJ/m 2 x 10-•) (GN/m 2 x 10-1) (Mj/m 2) U0 2.8 -+ 0.23* 6.7 +- 0.76 U1 2.8 -+ 0.32 7.0 -+ 0.86 U2 3.0 -+ 0.41 7.0 -+ 1.3 U3 2.9 +- 0.31 6.3 + 0.76 U4 3.1 -+ 0.45 6.6 -+ 1.0 2B0 2.6 +- 0.28 5.7 -+ 0.79 2B1 2.2 -+ 0.19 5.5 -+ 0.55 2B2 2.5 -+ 0.23 5.6 -+ 0.80 2B3 2.6 -+ 0.37 4.6 -+ 0.62 2B4 2.7 -+ 0.26 5.6 -+ 0.51 4B0 2.5 -+ 0.23 4.9 -+ 0.69 4B1 2.5 -+ 0.29 5.0 -+ 0.65 4B2 2.6 +- 0.35 4.7 -+ 0.74 4B3 2.5 -+ 0.23 4.6 -+ 0.50 4B4 2.9 -+ 0.29 5.6 -+ 0.66 4.4 +-- 0.71 3.3 +-- 0.31 2.6 + 0.31 -- 2.4 + 0.37 2.6 +-- 0.37 -- 3.4 -+ 0.64 2.5 -+ 0.58 -- 3.2 - 0.03 2.4 + 0.30 -- 3.4 + 0.46 2.4 +-- 0.40 3.8 +-- 0.79 3.0 +-- 0.32 2.3 - 0.30 -- 2.7 --- 0.26 2.1 +-- 0.29 -- 2.7 + 0.28 2.0 + 0.31 -- 2.7 +-- 0.33 2.0 --- 0.26 -- 2.9 + 0.32 2.4 +-- 0.46 2.7 + 0.27 2.8 +-- 0.32 2.2 + 0.32 2.8 + 0.32 2.9 + 0.36 2.3 --- 0.34 2.7 +-- 0.37 3.0 + 0.41 2.3 --- 0.34 2.6 q- 0.24 2.8 + 0.27 2.2 + 0.28 3.1 + 0.33 3.1 --- 0.32 2.6 --- 0.37 * 95% confidence limits.