350 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 160 140 120 E 100 80 60 - ß 20 ,,//• ' ..o- 0 20 40 60 80 100 120 HOURS Figure 10. Effect of pretreatment by Polymer JR on permeability of 0.1% sodium lauryl sulfate. Solid line: untreated. Dashed line: pretreated for 1 hr with 1% Polymer JR of 1% solution) and permeation of 0.1% SLS a time of some 60 to 70 hr is necessary before the permeability of the untreated membrane begins to rise sharply above that of the treated skin. This effect is reproducible as the repeated curves show. Even more striking are the results of Figure 11 at 10% SLS. Here significant differences are al- ready evident in less than 10 hr. An exact correspondence cannot readily be made to the conditions and times of the clinical testing cited above (11) but it is clear that these latter experiments involving prolonged occlusion and lasting for several days must represent many hours of effective contact with concentrated surfactant. These experiments of sorption and permeation begin to suggest a plausible mechanism for the action of the polymer on the stratum corneum. The polymer does not act pri- marily as a barrier to penetration of the surfactant since it has no influence on sorption. However, it does help to maintain the physical integrity of the membrane. That is, it seems to slow down the changes in structure which cause the greatly increased permea- tion as time goes on (Figures 7 and 8). The exact means by which the polymer strengthens the stratum corneum is not known at this time but it has been established

PERMEATION OF KERATINOUS SUBSTRATES 351 1.6 1.4 1.2 1.0 0.6 0.4 0.2 i 0 8 16 24 HOURS Figure 11. Effect of pretreatment by Polymer JR on permeability of 10% sodium lauryl sulfate. Solid lines: untreated. Dashed lines: pretreated for 1 hr with 1% Polymer JR that Polymer JR is itself highly substantive to stratum corneum (17). Its action may therefore be analogous to the glue-like property of cationic starches which are used to hold cellulose fibrils together in the paper-making process (21). CONCLUSION Diffusion studies have shown that penetration of (radiotagged) sodium lauryl sulfate, SLS, through neonatal rat stratum corneum is relatively rapid and increases with concentration even above the critical micelie concentration. Penetration by a cationic surfactant and a nonionic surfactant was also found but required a period of several days rather than hours as was observed for SLS. It is postulated that the high sorption and diffusion obtained with SLS are due in part to structural changes in the membrane brought about by this surfactant. These changes are mitigated by the preap- plication of a cationic polymer which was observed to reduce markedly the diffusion of SDS through the membrane.