PERMEABILITY OF EPIDERMIS 867 •oo, ooo NeL-5% / / //N•L-• % --, ! / • / /I I •.• I I ß • • ,oo.oool- , .. , N • / ß REC•ERY / • • (NoL-5 %) 0 2 4 6 8 fO •2 14 t6 18 20 2•2 24 26 f f hours) Ei• •0. [•ec[ o[ sodium ]•u•[e solutions on •[e• pe•me•bHJ[• by 1% aqueous sodium laurate (NaL) solution. The damage to the tissue continuously increases as reflected by the steepening slopes of the curve. No true steady state was observed in any of the experiments showing that the damage continues to occur. Pseudopermeability con- stants were computed at arbitrary times (indicated by small arrows) in order to help indicate the extent ot• the damage these are given on each figure. Increasing the concentration ot• NaL from 1 to 5% in- creases both the rapidity and severity ot• the damage (Fig. 11). It is interesting to note that the effect is not produced immediately but, de- pending on the concentration, develops after 9-6 hours. This suggests that the permeability of the laurate anion itself is rather small and that it must bind strongly with the tissue. Accurate permeability con- stants for the various forms of the laurate moiety are not available. 150,00C •3 100,000 * • 50,00C Sodium Louryl Sodium Lourote 5% Sulfote 5% / / ' , 59 • 10 -• •,.•"• ' H20 CO.Trol o 0 3 6 9 12 •5 f

868 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS But the lauryl sulfate anion in aqueous sodium lauryl sulfate (NaLS) was found to have a kp = 10 -5 cm/hr (13). The effect of these two sub- stances on the permeability of the tissue is similar, (e.g., Fig. 11) with NaL being more potent. Alkaline solutions buffered to the same pH as 5% NaL solution (pH = 10.0) had little effect. Water permeabilities before, during, and after the test runs of various reagent are listed in Table V. Sodium sulfate and acetic acid solutions of comparable ionic strength likewise had very little, if any, effect on permeability. Re- markably, concentrated urea solutions had no measurable effect regard- less of pH. This was also reported by Onken and Moyer (2). These data indicate that the laurate anion in the case of aqueous NaL and the lauryl sulfate anion in aqueous NaLS are the effective moieties. The recovery of the barrier function observed after removing the surfactant is depicted in Fig. 10 and also in Table V. Some of the membrane damage, particularly with the more concentrated solutions, is permanent but the recovery obtained is nonetheless remarkable. Permeabilities in the presence of laurate or lauryl sulfate anion were always considerably greater than after they were removed. The presence of NaL within the tissue also greatly reduces the amount of "bound water" as measured in water desorption experiments. These are identical to the experiments discussed earlier except that 570 aqueous NaL instead of pure water was used in the original hydration of the tissue. Results from a typical case are graphed in Fig. 12. Two identical samples from the same tissue were used both were soaked in 5% NaL (• -- NaL 5% , tt 5 hr immersion, then dialyzed in H20 5t hrs. 2 5 •) -- NaL 5%, tt 0 hr immersion, then desorbed without dlalys•s • t.0 (•) 0• o 14 1• 10 8 • 4 2 0 w/ WATER FRACTION IN TISSUE, f= • Wt Dry Dssue Figure 1•. Water desorption rate •s. amount o[ "bound water" in tissue alter treatment with NaL