282 JOURNAL OF COSMETIC SCIENCE sulfate or a mixture of ammonium lauryl ether sulfate and ammonium lauryl sulfate. Dynamic rheological measurements reveal that in all eight cases the salt effect is due to a variation in micellar relaxation time. The profile of the relaxation time vs. salt concentration was found to mirror the variation with salinity in measured entanglements per micelle. The roles of increased micellar branching, decreased micelle length, and increased micellar flexibility at higher salinity are outlined here. Mapping Penetration of Cosmetic Compounds into Hair Fibers Using Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) # Sidney B. H � mby*, Yohini Appa*, Si gr id Ruetsch , and YashKamath * Neutrogena Corporation, 5760 West 96 th Street, Los Angeles, CA 90045, USA # TRI/Princeton, PO Box 625, Princeton, NJ 08542, USA In this communication, penetration of vegetable oils into hair fibers has been investigated by the TOF-SIMS (Time-Of­ Flight Secondary Ion Mass Spectrometry) method. In earlier work [1], the method was found suitable to study the penetration of coconut and mineral oils into human hair. Therefore, the study has been extended to a gr oup of vegetable oils with different types of unsaturation in the fatty acid components. Different patterns of penetration have been observed for oils of different molecular structure. The general pattern which emerges from this study is that polyunsaturated oils do not penetrate at all, or do so only sparingly into the structure of hair. Most of these molecules seem to penetrate only into the cuticular region of the hair fiber. Oils with polyunsaturated fatty acids seem to have difficulty in penetrating hair. It is possible that these molecules do not fit into the fiber's cell membrane complexes, which are known to be the diffusion pathways in the keratin fiber. On the other hand, monounsaturated oils, such as olive oil, with more compact molecular structure seem to penetrate readily into the hair fiber. Experimental Testing and Numerical Modeling of Human Skin X. James Ren 1 , Chris W. Smith 2 , Ken E. Evans 2 , Paul J. Dooling3, Andrew N. Burgess 3 , Nabil Zahlan 3 , Anthony V. Rawlings 4 , and Johann W. Wiechers5 1 School of Engineering, Liverpool John Moores University, UK 2 School of Engineering, University ofExeter, UK 3 ICI Strategic Technology Group, Wilton, UK 4 AVR Consulting, Northwich, UK, and 5 Uniqema R&D, Gouda, The Netherlands In this feasibility study, changes in the elastic properties of skin following various skin treatments (e.g., water, skincare ingredients, etc.) were investigated using a new in vivo tensile testing method. The properties of human skin in vivo, and in particular the properties of the stratum comeum, were studied using a combined experimental-numerical approach. Tests on a small number of volunteers indicated that the in vivo testing method was sensitive to the effect of skin treatments and could distinguish their relative performances. The in gr edients tested effectively made skin less stiff. Preliminary results showed that stratum comeum is highly anisotropic and that the data was in general agreement with some but not all published in vitro results, although this is the first time ever that Poisson ratios for human stratum comeum are presented.