604 JOURNAL OF COSMETIC SCIENCE failure (i.e., more fibers are breaking after just a few fatigue cycles). This may indicate that as hair grows there are increasing numbers of fibers containing significant flaws that rapidly propagate and lead to fiber breakage. Data shows that both α- and β-values decrease from root to tip, indicating increased chance of breakage as hair grows longer and increased chance of premature breakage. An alternative way to show this data is to calculate the likelihood of failure after a given number of cycles from the Weibull distribution (Equation 1). Figure 3 shows the percentage chance of a fiber breaking at 500 cycles. This percentage is almost double at tips, 20.6% broken fibers after 500 cycles at tips versus 11.5% at roots. Panelists were asked several questions related to their habits and practices (e.g., use of shampoo, conditioner, and leave-on treatments, frequency of washing, use of heated implements, and chemical treatments). Specifically, the panelists were asked when they last colored their hair. No correlation of fatigue values was found with product use, wash frequency, or use of heated tools at either roots or tips. Figure 1. Root and tip α-values for 41 panelists. Figure 2. Root and tip β-values for 41 panelists.

605 FATIGUE STRENGTH OF PANELIST HAIR Some correlation was observed regarding coloring frequency but variability in individual α-values meant variability between groups was large. To reduce variability, α-values for each panelist response were averaged, indicating that time since last color does correlate with fatigue breakage (Figure 4). Panelists were asked “time since last color,” but if we assume that this can be translated into coloring frequency (i.e., longer time since last color equals a lower color frequency), these data indicate that a higher color frequency will increase fatigue breakage at tips. In addition, the decrease in breakage from root versus tip is also higher for colorers (40% for past 4-week colorers versus 10% for noncolorers). This fits with anecdotal information from consumers (i.e., those who color more frequently also claim that hair breakage is an issue for them). Figure 3. Percent probability of breakage at 500 cycles. Figure 4. Fatigue α-value versus time since last color.