hair Tensile Strength

The cosmetic industry places a great deal of emphasis hair strength, yet the goal of finding an ingredient that strengthens hair in a consumer-noticeable way is as yet unachieved. However, for the clinician tensile strength is of little value except to prove the obvious, i.e., that damaged hair is weaker, or to disprove a claimed patient history. It is well known that chemical treatments weaken the hair fiber. In experienced hands the shape of the tensile stress–strain curve can give insight into how the fiber has been treated. But for the clinician who has been told that the hair has been permed or straightened it is no surprise to fi nd a reduced tensile strength. Tensile strength measurements also require large sample numbers (~100 fibers), diameter measurements for each fiber, and a high degree of expertise. Hence, they are of little added value to clinicians.