18 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 30•018 b 3000X c lOOOX . . 2000X 3500X Figure 4. a--c. Highlights of cuticular damage observed in autofluorescence in a light microscope. a: Untreated extended hair fiber. b: Typical view of an untreated hair fiber extended to --20%, displaying the start of scale edge lifting. The increasing magnifications of c show a high level of scale lifting of surface cuticles, scale buckling, and cracking. The high magnification clearly displays the torn-off endocuticular material underneath the lifted cuticle. Endocuticular failure results in scale edge lifting. frozen in that position even after relaxation in water. Manifestations of the previously imposed stresses that brought about the scale lifting, buckling, cracking, and in some cases the appearance of exposed endocuticular and intercellular materials can still be seen on the fiber surface. It appears, therefore, that while recovery of the cortex and reversal

STRESS RELEASE IN HAIR CUTICLE 19 6000X .. 3000X 1000X 2000X ., ..... • 3000X 2800X Figure 4. d-h. d: A high level of scale lifting and torn-off endocuticular material underneath the lifted surface cuticle. e: Extension-induced, jagged tear lines. f.' Severe cracking, buckling, and lifting of the surface cuticles and unexplained "plugs," possibly connecting points between cuticle and cortical cells. g: Splitting between the surface cuticle's exocuticles A and B, resulting in scale lifting. h: The endocuticular layer as surface structure, after epicuticle and exocuticles A and B were worn off. of the ot-[3 transformation may indeed by complete, the cuticular damage experienced during extension up to 32-36% is not reversible. We have explored the recovery of the mechanical properties of human hair root and tip sections from 30% extension followed by release and immersion in water for 20 hours. The data shown in Table 1 show very little difference in the mechanical properties between root and tip section, and indicate extensive, although not total, recovery of the