2008 TRI/PRINCETON CONFERENCE 93 cells are decemented, they can buckle and deform in water by swelling stresses even if their deformations were previously recovered. EFFECTS OF OIL PENETRATION INTO GAPS AND CAVITIES When Jojoba oil or any other oil was applied to lifted cuticle cells presenting gaps or cavities it did not lead to deformation recovery. Thus, oils did not induce plasticization of the cuticle cell proteins. The oils, however, were seen to penetrate into gaps and cavities destroying the light interference patterns. Gaps and cavities protruding away from the hair surface were still visible by optical microscopy after oil penetration even when their associated patterns of light interference were destroyed. This is as expected since air in the cavities has been substituted by oil a material with a higher index of refraction than air. In Figure 9 it can be seen, for instance, that cavities and gaps produced by lifted and buckled cuticle cells are still visible even when their patterns of light interference have been destroyed by the presence of oil. In contrast, oil penetration concealed gaps and cavities existing deep inside the cuticle sheath with no associated surface protrusions. Figure 10a,b shows, for instance, that gaps and cavities not involving cuticle cell protrusions were not longer visible by optical mi- croscopy after oil penetration. Thus, oil impregnation of these cavities gives the appear- ance that the hair surface doesn’t have any damage or any defect at all (see Figure 10b). These observations confi rm the previous hypothesis proposing that damage by grooming stresses produces gaps and cavities that later are fi lled and concealed by the penetration of lipids, either, from sebum or from cosmetic formulations. It is worth to mention here that other researchers have found that Jojoba oil does not penetrate into the cortex although the experiments here show that it can penetrate in cavities formed at the cuticle sheath (10). EFFECTS OF WATER AND OIL PENETRATION INTO GAPS AND CAVITIES As shown in previous paragraphs water induces a rapid mechanical recovery of the de- formed protein structure within the cuticle sheath, while oil penetrates into these defects. Figure 9. Micrographs (300×) of a hair fi ber with decemented and buckled cuticle cells before (9a) and after (9b) immersion in a solution of 0.1% Jojoba oil for 3 min. Observe that the oil has penetrated underneath the buckles or cavities but that the cuticle cell deformations remain.

JOURNAL OF COSMETIC SCIENCE 94 Both phenomena were seen to lead to the disappearance of gaps and cavities water by deformation recovery while oil by cavity impregnation. Possible benefi ts and effects re- sulting from the occurrence of both phenomena are analyzed in the following sections. As it was mentioned before cavities formed by cuticle cell buckling close once recovered by water immersion. The cavities could, however, be reopened again after the hair fi bers were dried and immersed in water at alkaline pHs. This phenomenon of lifting and reopening took place while the hair fi bers were immersed in water and was ascribed to the action of unbalanced water swelling stresses in dece- mented cuticle cells. Further, analysis showed, however, that the degree of cuticle cell lifting and reopening at alkaline pHs was substantially reduced if the cavities were im- pregnated with oil previous to their recovery process with water (see Figure 11a,b). In the absence of oil treatment the degree of cuticle cell reopening was higher. Figure 11. Micrograph (250×) of two hair fi bers with buckled and recovered cuticle cells showing degree of cuticle lifting while immersed in water at pH 10.0. One fi ber was immersed into the alkaline water without oil treatment (a), while the other (b) was treated with oil before the buckled cuticle cells recovered. Figure 10. Micrographs (300×) of a hair fi ber showing agglomerations of cavities without bulging before (a) and after (b) it was immersed in a solution of 0.1% Jojoba oil for 3 min. Observe that the oil has penetrated and impregnated the air cavities, concealing them and destroying the light interference phenomena.