Hair Breakage 260 in the end user. It is often suggested that the fragility of Afro hair results from an increased presence of flaws within the fiber structure which are a consequence of high stress points within the highly kinked conformation. While this hypothesis sounds reasonable, we are unaware of any data in its support. Conventional stress- strain testing on virgin, single source Afro hair (obtained from International Hair Importers, Glendale, New York) showed the break stress and break extension to be approximately 13% lower than virgin Caucasian hair tested under the same conditions. Therefore, there is evidence to back up the “weaker” state of this Afro hair, although the magnitude of this difference would not seem sufficient to cause such dramatically different user habits. Figure 6 compares S-N curves for this Afro hair relative to Caucasian hair under the same conditions shown earlier. Two observations stand out from these results. Firstly, the regression line for Afro hair falls noticeably below that of Caucasian hair. Indeed, while conventional stress-strain experiments suggested Figure 5. Average cycles-to-fail for Caucasian hair at 60% RH as a function of fiber dimension and repeating load