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© 1998 Society of Cosmetic Chemists
Journal of the Society of Cosmetic Chemists, Vol. 49, No. 3, 141-153

The cracking of human hair cuticles by cyclical thermal stresses
Manuel Gamez-Garcia



Cycles of wetting and blow-drying were applied to hair fibers and resulted in the formation of multiple cracks on the hair cuticles. The peculiarity of these cracks was that they always appeared aligned parallel to the longitudinal axis of the hair fiber. The cracks appeared to be initiated at the end of the cuticles close to the cortex and propagated invariably towards the outer cuticle edges. The maximum growth length of each crack was seen to be limited to the size of one cuticle. Crack formation did not only occur at the outer edges of the cuticles but also took place in the second and third overlaid hidden cuticle sections. The results show that these cracks form when the external portions of the cuticles undergo drastic reduction in their hydration water. Under these conditions the outer cuticle portions become rigid and brittle and crack by the action of circumferential tension stresses arising from the swelling pressure of both the cuticle layers underneath and the cortex itself. Hair cuticle analysis from a panel of 100 individuals showed that these cracks are present in the hair of people who commonly blow-dry their hair and appear to a much lesser extent in the hair of subjects who do not practice this type of grooming process. The combing of hair fibers presenting this type of cracking was seen to result in the breakage of large portions of cuticle. The effect of some cosmetic actives on the formation of these cracks is also discussed.

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© 1998 Society of Cosmetic Chemists
Journal of the Society of Cosmetic Chemists