PERMEABILITY OF EPIDERMIS 869 Table V Effect of Surfactants on the Permeability of H20 Permeability Constants for H•O (k v X 10 a cm/hr) Solution Before Test Run a After (4 hr) 5% NaL (pH 10.2) 0.25 61.3 0.18 43.3 0.22 38.6 0.18 88.8 (6 hr) 1% NaL (pH 9.8) 0.20 31.4 0.22 42.5 0.22 49.6 0.18 61.6 (12 hr) 5% NaLS (pH = 7.0) 0.18 31.4 0.23 46.5 0.22 38.5 0.16 39.8 (20 hr) 1% NaLS (pH = 7.0) 0.28 14.5 0.62 12.3 0.19 9.1 0.43 11.9 Buffer (pH 10.2) Ionic 0.61 0.78 str. -• 0.68 0.69 0.96 0.44 0.66 0.56 0.94 5% Na•SO4 (pH = 7) 0.22 0.18 0.47 0.76 5% Acetic acid 0.21 0.43 0.25 0.51 ... 26.8 ... ß.. 18.9 ... ß.. 35.1 ... ß.. 35.5 ... (10 hr) (8 hr) (45 hr) 90.2 9.8 6.2 90.3 7.4 4.4 83.8 6.3 4.1 78.5 7.2 5.5 (55 hr) 4.7 3.5 3.1 3.2 4.2 7.0 5.9 8.3 5.1 6.7 4.5 5.0 2.9 3.6 2.0 3.4 0.14 0.89 0.35 O.44 a Since the surfactant solutions continued to damage the membrane during the experiment, the kp values given for each test run arc permeability constants taken from the slopes of the curves at the times indicated other permeability constants arc truc steady state values. For example, all the kp'S in the presence of 5% NaL wcrc taken after 4 hours. solution for approximately 11 hours. Sample 1 was placed in pure water while still wet from the soap solution, sample 2 was used im- mediately in the desorption experiment. After sample 1 had soaked in water for 51 hours and the soap had largely been removed, its de- sorption behavior was recorded. Comparison of the data shows that

870 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VI Bound Water in Stratum Corneum Initial Final Bound Dry Wt Dry Wt H20 Immersion Time Sample (mg) (mg) Ratio (hr) No. After NaL 5% After rehydration of dried, NaL-containing tissue After NaL 5% and im- mediate dialysis 0.70 1.06 0.14 24 • 110 0.75 1.15 0.27 24 113 0.78 ... 0.75 24 117 0.78 1.18 0.22 24 120 0.80 1.37 0.30 24 123 1.17 ... 0.51 24 32 1.20 ... 0.69 7.5 31 1.60 . .. 0.66 7.75 15 Soap H20 1.17 0.90 0.75 24 72 32 1.20 0.92 1.09 7.5 24 31 1.60 1.40 0.94 7.75 27 15 0.78 0.40 5.67 24 24 114 0.79 0.48 7.72 24 24 118 0.75 0.47 7.95 24 24 119 1.52 1.06 4.33 48 80 19 2.25 1.34 6.82 11.5 51 43 1.22 0.82 8.28 5 51 28 1.06 0.82 4.87 3.5 57 30 the capacity of the tissue to retain large amounts of bound water is radically reduced in the presence of the soap and is restored when the soap is removed. The data from similar experiments are recorded in Table VI. It is interesting to note that if the soap is allowed to dry in the tissue it becomes very firmly incorporated and very difficult to re- move. Subsequent soaking in water will not restore the ability of the tissue to bind water, e.g., samples 32, 31, and 1/5. Mechanism o[ Action o[ NaL on Stratum Corneum After soaking a disc of stratum corneum in 5% NaL for 24 hours, a visible expansion in the plane of the tissue can be detected. This con- tinues for 48-72 hours and the expansion in area can be as great as 50-80%. The expansion of isolated epidermis after treatment with surfactants was reported earlier by G6tte (14). As is well known, the stratum corneum is a lameliar structure consisting of approximately 10-15 interdigitating layers of flattened, a-keratin-containing cells. Within the cell the a-keratin filament.•, imbedded in an amorphous matrix of