608 JOURNAL OF COSMETIC SCIENCE weak correlation at roots. However, using the mean scores for each coloring time point,, a good correlation for tips is seen between fatigue α-value and FTIR score (R2=0.73) and cuticle SEM damage score (R2=0.77). The FTIR score at tips also strongly correlated with cuticle SEM damage score (R2=0.91). This correlation implies oxidative damage also weakens hair to fatigue breakage in panelist hair samples, as seen in lab created tresses (2). The panelist variability in fatigue breakage at roots did not strongly correlate with oxidative damage and this is likely related to differences in hair structure. Cuticle damage was minimal in the first 6–8 cm of growth and oxidative damage was relatively low even for panelists who color regularly. Previously published data show that internal lipids can influence fatigue strength and hair can be strengthening via the addition of lipid materials (e.g., cetyl and stearyl alcohol) (3). Camacho-Bragado proposed a technical model where failures in the lipid-rich cell membrane complex structure play a key role in breakage of curly hair (10). In this study, internal lipid levels and composition were quantified using a differential extraction method. First, hair samples were cut into 5 cm lengths from root to tip and then extracted with hexane to remove surface lipids. A second extraction was then performed with chloroform–methanol to remove internal lipids and this extract was then analyzed by gas chromatography. As expected, most lipids extracted were fatty alcohols (∼80%) along with cholesterols, wax esters, and squalene from sebum (11). A reasonable correlation in internal fatty acid levels with fatigue breakage at roots was observed with R2=0.36 (Figure 9) supporting the hypothesis that lipid levels are important for fatigue breakage. Lipid levels do not explain all the root hair fatigue breakage, indicating that Figure 8. Correlation of fatigue α-value with (A) FTIR cysteic acid and (B) SEM cuticle grading score. Figure 9. Correlation of internal fatty acid levels versus fatigue α-value.

609 FATIGUE STRENGTH OF PANELIST HAIR protein differences may also be contributors. More work is required to confirm this hypothesis. No correlation is seen for lipid levels at tips, likely due to additional damage that contributed to fatigue breakage. ASIAN PANELIST RESULTS The Asian panelist’s hair samples were all between 30 and 45 cm long and all very straight. Table I shows the cysteic acid and fatigue resuts for root and tip hair as well as the coloring/ bleaching and perming details. In general, there were similarities between the Asian and Caucasian panelists. As oxidative damage increased, either by coloring or powder bleaching, fatigue cycles to break decreased, especially panelists using powder bleaches. The oxidative damage was much higher for a powder bleach as compared to the oxidant in a Level 3 permanent colorant and, with the exception of panelist S09, the α-values were 1,000 or less at tips. S09 had a relativly high α-value although she had a powder bleach and she also had a much higher α-value at tip than at the roots. This was also seen in S73 and S79, but there was nothing obvious in the given habits and practices information that would explain this. Additional fatigue fibers were run to ensure this difference was significant and not a sampling issue. As with the Caucasian panelists, the α- and β-values mostly decreased from root to tip, meaning the probability of breakage and chance of premature failure of fibers increased at tips. The wide variation of α- and β-values was also similar. CONCLUSION Breakage is a concern for many consumers, especially those with long hair. In this study, analysis of panelist hair indicated that regular use of permanent coloring or powder bleaching products can lead to increased breakage, as measured using a fatigue protocol where hair was subjected to repeated low-level stress. Fatigue breakage was also found to correlate closely with measured damage by two methods: FTIR cysteic acid and SEM cuticle damage score at hair tips where damage is at its most advanced. As expected, fatigue breakage also Table I Panelist FTIR and Fatigue Values Root and Tip Panelist number Coloring habits Perming habits FTIR cysteic acid Fatigue α-value (63.2% cycles to break) Fatigue β-value Root Tip Root Tip Root Tip S71 Uncolored No 0.15 0.26 3,783 3,381 2.68 0.71 S78 Uncolored No 0.15 0.19 7,050 5,909 1.43 1.46 S79 Uncolored No 0.19 0.20 4,432 16,867 1.66 1.39 S52 Level 3 Colorant Yes 0.19 0.24 9,111 5,835 0.61 0.81 S35 Level 3 Colorant Yes 0.43 0.67 12,694 11,201 1.93 0.62 S73 Level 3 Colorant No 0.35 0.57 8,846 25,616 1.83 0.67 S07 Powder Bleach No 0.21 1.03 2,173 773 1.92 0.81 S09 Powder Bleach No 0.80 0.78 5,490 16,266 2.07 0.83 S25 Powder Bleach No 0.17 1.19 2,929 798 1.73 1.45 S100 Powder Bleach Yes 1.27 1.29 403 150 0.72 0.84 S107 Powder Bleach No 1.27 1.19 512 1,067 0.65 0.63 S112 Powder Bleach No 1.34 1.35 1,025 420 0.86 0.60