POLYMERS AND LIPIDS ON SKIN BY ESCA 301 Table III Surface Composition of Polymer-Treated Skin Samples--Substantivity on Unwashed Skin Atomic % Polymer C O N P S Si C/O Polyquaternium- 10 Outer 84.2 11.2 2.7 N.D. N.D. 1.3 7.52 Inner 81.7 14.3 2.7 1.3 N.D. N.D. 5.71 Polyquaternium-24 Outer 75.9 19.6 1.3 N.D. N.D. 3.1 3.87 Inner 80.6 16.9 1.4 0.6 N.D. 0.2 4.77 Chitosan Outer 79.9 13.4 3.9 N.D. 0.1 2.7 5.96 Inner 79.4 16.3 2.8 1.2 0.2 0.1 4.87 All entries are average of two separate samples. N.D. = not detected. longed exposure to the polymer solution may result in some lipid loss from this side of the membrane with concurrent polymer deposition. Alternatively, this inner surface may present a more "porous" or less keratinized substrate which the polymers can diffuse into with relative ease. A further clue to this behavior is offered by the changes in phosphorus content detected on these samples. As shown in Table Ill, treatment of these unwashed skin samples in the polymer solutions results in a shift in the relative levels of phosphorus on the inner and outer surfaces as compared to the untreated controls (Table I). This may indicate the loss of a water-soluble phosphate compound from the outer surface and, conversely, exposure of a nonsoluble phosphate lipid on the inner surface by removal of other sol- uble materials. It seems likely that these observed changes in phosphorus content are linked to changes which occur upon prolonged contact of the membranes with water, in turn altering the receptivity of the inner surface to the polymers. The data obtained from skin samples exposed to the polymer solutions following treat- ment with an SDS are given in Tables V and VI. Polyquaternium-24 exhibits roughly equivalent performance on these samples versus the previous unwashed set. However, the modification of the membrane surface upon removal of the lipid layer by the SDS completely overwhelms any orientation effects and results in clear deposition of Poly- quaternium-10 and chitosan regardless of the membrane surface examined. (Any re- sidual SDS on the surface of the membrane could, of course, influence the adsorption of a polycation, but we do not believe this to be the predominant effect following SDS washing.) All measures of surface polymer adsorption, C/O ratio, alcohol/ether content, and quaternary nitrogen, yield roughly equivalent results on both sides of the SDS- washed membranes. It appears, then, that Polyquaternium-10 or chitosan can best adsorb when the original lipid mantle has somehow been disrupted, e.g., by exposure to harsh surfactants or other skin irritants (6). In order to provide a semi-quantitative measure of the degree of polymer surface cov- erage achieved with each of these treatments, a fractional surface coverage was com- puted using equation 1: Measured C/O = X (Polymer C/O) + (1 - X)(Skin C/O) (1)

302 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table IV Substantivity on Unwashed Skin--High-Resolution Results Atomic % C N Polymer CH C - O C = O COO N N + P olyquaternium- 10 Outer 68.5 9.6 3.6 2.6 2.7 N.D. Inner 60.4 15.6 4.6 1.0 2.0 0.7 Polyquaternium-24 Outer 53.1 17.8 3.7 1.5 0.7 0.4 Inner 53.4 23.4 3.7 0.3 1.0 0.4 Chitosan Outer 59.6 12.8 4.4 3.1 3.9 N.D. Inner 56.4 16.4 4.7 1.8 2.0 0.8 All entries are average of two separate samples. N.D. = not detected. The skin C/O ratios were obtained from the control data, while those of the polymers were calculated on the basis of the known molecular structures. In making this calcula- tion, the assumption is made that the polymer-treated surface is composed of interdis- persed regions with a polymer coating and regions of uncovered skin. The results of these calculations (Table VII) generally confirm the qualitative observa- tions previously discussed. Only Polyquaternium-24 exhibits measurable adsorption on the unwashed outer skin surface, while all three polymers adsorb on the inner surface. Following a preconditioning SDS wash, each adsorbs equally well, irrespective of the particular skin surface tested. The assumption made in this calculation is that polymer deposition is the only process Table V Substantivity of Polymers on SDS-Washed Skin--Surface Compositions Atomic % Polymer C O N P S Si C/O Polyquaternium- 10 Outer 74.2 18.8 5.4 0.1 1.2 0.2 3.95 Inner 70.8 17.4 7.4 0.9 1.0 0.4 4.07 Polyquaternium-24 Outer 74.7 18.6 4.8 0.3 0.6 1.0 4.02 Inner 70.3 19.2 8.6 0.7 0.6 N.D. 3.66 Chitosan Outer 74.6 16.7 7.0 0.2 1.5 N.D. 4.47 Inner 73.4 16.0 7.6 0.6 1.2 0.2 4.59 All entries are average of two separate samples.