40 JOURNAL OF COSMETIC SCIENCE MORPHOLOGICAL CHANGES IN HUMAN HAIR CUTICLES UPON THE SIMULTANEOUS ACTION OF CYCLICAL MECHANICAL AND THERMAL STRESSES THEIR RELEVANCE TO GROOMING PRACTICES Manuel Gamez, Ph.D. Croda North American Technical Center, 180 Northfield Avenue, Edison, NJ 08837-3873 INTRODUCTION A hair cuticle analysis suggests that cuticle damage patterns in non-chemically treated hair can be reproduced by the appropriate application of several cyclical thermal and mechanical stresses. Common patterns of cuticle degradation such as cuticle de-cementation, cuticle lifting, shape distortion, vertical and horizontal cracks, and fine and coarse irregularities at the cuticle edges (1-3) are also shown to relate to different grooming practices. METHODOLOGY The cyclical strain levels used in these experiments were found to be the minimum levels necessary to reproduce the damage patterns described above. Fifty cycles of 7 % deformation under extension were applied to virgin hair fibers with a Diastron tensile tester in the automatic mode. The cyclical torsion strain levels •vere those resulting from imposing 20 turns per inch to the hair fiber, both, in the clockwise and counterclockwise mode for 25 times in each mode. Twenty cycles of thermal stresses consisting each in 10 seconds of dry blowing followed by 10 seconds of water immersion were applied to single fibers. A commercial blow dryer was used and it was placed 8 cm a•vay from the fiber. In some cases the cycling experiments were carried out at three different humidities, namely: 15, 60, and 80 % RH. For abrasion studies an in-house made combing wheel was used. RESULTS AND CONCLUSIONS Cuticle de-cementation: Portions of lifted and de-cemented cuticles and random small horizontal cracks about 10 microns long were the result of pure cyclical extension stresses (see Fig. la). The cuticle lifted patterns resembled those already observed by S. B. Ruetsch et. at. (2). This type of cuticle damage was more severe at 15 % RH than at 50 % RH, and above 80 % RH no more cuticle de-cementation nor cuticle lifting was observed, only occasionally long transversal cracks were apparent. Cuticle cracking: Cuticle cracking was seen to take place only when any of the following cyclical stresses were applied: 1) Thermal stresses, 2) Torsion stresses at low humidities (15 % RH), and 3) Extension stresses at humidities (I5 % RH). Thermal cyclical stresses produced multiple vertical cracks whose extension was seen to be confined to a single cuticle (see Fig. lb) These types of cracks were only produced in new cuticles and their number diminished or vanished in severely abraded cuticles. Pure cyclical torsion stresses at low humidities were found to produce long cracks 10 to 50 microns long which appeared forming 30 to 50 degrees angles with the longitudinal axis of the hair (see Fig. 2). Cyclical extension stresses, on the other hand, resulted in small horizontal cracks 5 to 10 microns long which were randomly distributed along the fiber. Cuticle fusion: This term is used to describe cuticle damage characterized by the loss of cuticle boundaries and cuticle structure in general, it was found after the application of cyclical torsion stresses (see Fig. lc). Cuticle Abrasion: Two types of abrasion were found to take place, the first one occurred when the cuticle was still cemented and took place by the removal of fine powdery portions at the edges of the cuticle. This type of abrasion left the cuticle edges regularly

PREPRINTS OF THE 1997 ANNUAL SCIENTIFIC MEETING 41 spaced. The second type of cuticle abrasion took place after the cuticle had been cracked or de- cemented and was characterized by the removal of big potlions of cuticle (2). Both types of abrasion have been repotled in the past (2-3). Cuticle shape distortion: Open ripples, bulges, bumps, and crater formation were among the main forms of cuticle distortion found after cyclical stresses. The formation of open ripples by the cuticles was ohsended after extension cyclical stresses (see Fig. 1), while the combination of thermal and extension cycles lead to the formation of bulges, bumps, and crater formation (see Fig. ld). Finally, the analysis showed that hair cuticles of persons who use a blow dryer contain a great number of thermal cracks, while the hair cuticles of persons who blow dry their hair while simultaneously combing it show open cuticle ripples with thermal cracks superimposed on them. Iron curling, blow drying and combing practices were seen to result in cuticles with bumps, bulges, vetlical cracks, and irregular cuticle edges. REFERENCES (1) C. R. Robbins, "Chemical and Physical Behavior of Human Hair", 3rd ed. (Springer-Verlag, New York, 1994) pp. 211-226. (2) S. B. Reutsch and H. D. Werigmann, J. Soc. Cosmet. Chem., 47, 13-26 (1996) (3) J. A. Swift, Int. J. Cosmet. Sci., 13, 143 (1991) i I,, 1200X 1140X •,• . 1450X ld Fig. 1 a-d) la, Cuticle de-cementation lb, Thermal cracks lc, Cuticle fusion, ld, Cuticle bumps, bulges and crater formation.