Chapter 14 473 this effect. Furthermore, Kamath and Weigmann44 observed that wetting and combing hair tresses provides a large increase in the mid-length force and at the same time a decrease in the end peak force compared with combing dry hair (65% RH). A few years later, Robbins and Kamath38 observed more short segment breaks in dry versus wet combing, but more long segment breaks in wet combing. Furthermore, cross-cutting hair and combing it dry versus a tapered cut provides even higher end peak forces and more short segment breaks.45 These results confirm that combing forces correlate with hair breakage, but more importantly the location on the fiber where hair damage and breaks occur actually corresponds to where higher combing forces occur on combing force curves. In other words, mid-length combing forces correspond to long segment breakage and the end peak force corresponds to short segment breakage. Changes in hair fiber properties as individuals age likely impact hair breakage. Robbins and Reich46 have shown that combing forces are related to hair fiber properties in the following manner. Combing forces increase with fiber curvature (quadratic relationship) and with fiber friction (linear relationship), but they decrease with fiber stiffness (linear relationship which is collinear with diameter). Smaller diameter hairs break more readily than larger diameter hairs because they are less stiff and they bend and tangle more readily. Therefore, for many female adults, hair breakage concerns should increase when they reach their forties when fiber diameter begins to decrease.15-20 Changing straight to wavy hair has little effect on combing forces, which are determined primarily by fiber friction and diameter in that curvature range. However, as hair waviness increases to curly, combing forces increase and hair breakage increases even more.43 Since most current cosmetic hair treatments produce negligible effects on fiber diameter and stiffness, combing forces for straight to wavy hair are dominated by fiber friction. This is why hair conditioners are so effective in reducing combing forces and breakage for Caucasian type hair, and in that manner hair conditioners make hair more resistant to grooming actions, i.e. stronger.