ABSORPTION OF CHEMICALS ON SKIN Blank's results however, we extracted up to 17% material from callus with various organic solvents when the callus was previously swollen in water. Table I indicates the solvent systems used and the weight losses obtained. These experiments indicate that other materials besides lipids are extracted from callus with organic solvents and the assistance of water. Extraction of Water-Soluble Substances from Callus by Surfactants The following surfactants were examined: sodium lauryl sulfate, sodium lauroyl isethionate, polyoxyethylene sorbitan monostearate (Tween 80),* cocoyl sarcosine, and sulfated ethoxylated fatty alcohol. Sodium lauryl sulfate and sodium lauroyl isethionate were chosen to allow direct comparison with the results obtained by Middleton (15) who worked with guinea pigs' footpads. He found a somewhat greater extraction of water-soluble substances by the use of sodium lauryl sulfate than by the use of sodium lauroyl isethionate: 9.5% versus 7.9%. We found increased extraction by isethionate this was more pronounced at higher concentrations (Fig. $). The immersion time for the various callus pieces was 24 hours, and the drying time was g days. Thus, different surfactants had different solubilizing capacities, and these became more evident at higher concentrations. At the lower sur- factant concentrations, there may have been an overlapping between *Atlas Chemical Industries, Inc., Wihningtou, Del. 19899. • +• o, _z o -- Lu •: -25 © SODIUM LAURYL SULFATE [] SODIUM LAUROYL ISETHIONATE 0.075 0.15 MOLAR CONCENTRATION Figure 3. Weight gain or loss after drying of experimental moieties of callus immersed 24 hours in surfactant solutions of different concentrations as compared to the weight loss of the control callus moiety immersed in water

144 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Water Retention of Callus Halves Immersed in Tween 80, or Water, and Dried Weight Change," (%) Drying Time 5 min 80 rain 1 day 5 days 1st Immersion (22 hours) 30% surfactant 230.0 58.4 Water 212.2 37.9 50% surfactant 114.2 42.8 Water 155.0 46.0 2nd Immersion (48 hours) 30% surfactant 326.0 Water 302.0 50% surfactant 128.0 Water 209.0 6.4 --16.3 --2.6 --6.1 2.3 --8.6 --4.5 --4.5 a Minus sign indicates weight loss. surfactant absorbed in stratum corneum and extraction of water solubles from callus. At the higher concentrations, it appeared that some sur- factants had greater solubilizing capacity than others. Table II summarizes results obtained with Tween 80. With a 30% Tween solution, callus absorbed more water than callus immersed in water. With a 50% Tween solution, the opposite took place. Callus immersed in 30% Tween solution retained more material all the way through the drying cycle. With the 50% Tween solution, there was less water retained by callus through the drying cycle than with water. It does not seem from the weights after 1 and 5 days' drying time, that Tween was absorbed by callus. Thus, differences in ultimate weight gain or loss and differences in water-retention capacity were observed according to the concentration of this surfactant. This finding is interesting, since the same compound can be used in a concentrated form as an ointment, or diluted as a component in a cleansing formulation. Table II shows a duplication of effect when the operation was repeated although the length of immersion the second time was 48 hours instead of 22 hours. Cocoyl sarcosine dispersions ranging from 1 to 20% concentrations were chosen as representative of an acidic surfactant system. The pH of these dispersions ranged from 3.1 to 3.8. Results are summarized in Table III. As can be noted, a high amount of weight gain represents a high amount of cocoyl safcosine absorbed by the stratum corneum. As the concentration was increased to 20%, the callus weight after drying