251 Chapter 8 Hair Breakage Trefor Evans TRI-Princeton Introduction The presence of broken fibers can be a major detractor in the quest for beautiful hair. For some, just seeing broken fragments in a brush or comb can be a source of worry. This is largely because broken fibers fray and lead to the formation of unsightly split ends but also, hair no longer aligns as readily, often reducing the perception of hair smoothness, inducing a degree of frizz, lowering shine, and hindering a fluid flowing motion. Therefore, consumers are very concerned about breakage and look to product manufacturers for help. Attempts at aiding this issue begin with a better understanding of the problem therefore, the objective of this chapter involves summarizing what’s been learned from ongoing research into the causes of breakage and the relative contribution of various factors. The previous chapter highlighted methodologies for probing the mechanical properties of hair and discussed the use of constant- rate extension experiments to generate stress-strain curves. In short, testing involves stretching individual hairs to their breaking point, while a load cell measures the internal forces generated within the fibers. These experiments are commonly used throughout the industry to illustrate how external factors (e.g. chemical treatments, such as coloring, perming, relaxing, exposure to the sun’s UV