606 JOURNAL OF COSMETIC SCIENCE Two other measures of damage were performed on the same 41 panelists: cysteic acid measurement using FTIR and cuticle integrity using a SEM damage scale. Cysteic acid is an industry method that has been shown to correlate with oxidation from colorants and bleaches (8). It is a nondestructive method that quantifies formation of cysteic acid via the S–O stretch at 1,040 cm-1. This study measured every 5 cm down the hair from root to tip. As expected, panelists who claimed to have never used hair color showed only a slight increase in cysteic acid (∼10%, likely due to UV oxidation). Panelists who had colored in the last year or more frequently showed a much higher level of increase. Average cysteic acid values increase for mid and tip hair as time since last color decreases (Figure 5). This supports for our assumption that time since last color can be corelated with frequency of coloring. No difference is seen for root hair other than an increase for the group who colored in the last 3 mo. All other groups had noncolored regrowth at their roots and showed a low FTIR score. We did not see a linear increase in FTIR score from root to tip and the mid value was consistently only about 10–20% lower than the tip value. This may be due to not all-over coloring habits or, more likely, due to cuticle removal via brushing/combing. The FTIR method only measures surface cysteic acid (penetration depth 2–5 µm) and overall cysteic acid decreases or flattens as cuticle with high-cysteic acid is physically removed. Cuticle damage was assessed via SEM grading where 25 fibers at mids and tips were graded on a four-point scale. Low damage: cuticle aligned and spaced regularly but some irregularity or slight lifting of the cuticle is observed (up to ∼15% lifting). Mid damage: cuticle is irregularly spaced due to missing cuticle edges, but all cuticle is present is tightly packed with lifted cuticle edges. High damage: any cuticle missing up to 50% of fiber significant cuticle chipping and partial removal of cuticles. Stripped: majority of fiber stripped (must be 50%). HDSS was calculated from this grading to calculate a single number: HDSS = (1× low) + (3× medium) + (5× high) + (7× stripped)*(100/175). Figure 6 shows example images of each grade. Cuticle damage was minimal at mids but increased significantly at tip (Figure 7). The increase was notably higher as time between Figure 5. Cysteic acid FTIR value versus time since last color.

607 FATIGUE STRENGTH OF PANELIST HAIR color decreased (i.e., as color frequency increased cuticle damage also increased). Cuticle removal increases as consumers color more frequently because oxidative damage increases and more disulfide bonds and other protein bonds are broken. Hair subjected to extensive oxidative damage has also been previously shown to have higher propensity for physical damage (9). These two well-established damage measures were then correlated with fatigue breakage data (Figure 8) for tips. SEM grading was not performed at roots and FTIR showed a very Figure 6. Example images for SEM grading scale. (A) Low damage, (B) medium damage, (C) high damage, (D) stripped. Figure 7. SEM cuticle damage score versus time since last color.