Chapter 5 185 Beideman86 used a thermomechanical analyzer to measure depilation times. Both Elliot and Beideman report consistent results that are useful for evaluating depilatory efficacy, but their methods require either specialized or expensive equipment. My colleague Robert Mermelstein and I used the SFTK method to study depilatory efficacy.31 Figure 18 shows SFTK curves for two commercial depilatories. We found that product A was faster than product B for removing hair from human legs in vivo. Rather than analyze these data for rate constants, as was done with permanent waving systems, we concluded that the time to reduce the normalized force by 95% (T 95 ) Figure 17 A. Rate of cross-sectional and longitudinal swelling B. Extent of longitudinal swelling. Modified from Yablonski and Williams with permission of the Society of Cosmetic Chemists.83