ABSORPTION OF CHEMICALS ON SKIN I45 Table III Water Retention of Callus Halves Immersed in Cocoyl Sarcosine? or Water, and Air-Dried Weight Change b (%) Drying Time 15 min 1 hour 24 hours 1% surfactant 194.5 159.5 7.3 Water 213.0 98.3 -- 27.1 3% surfactant 153.0 133.5 17.1 Water 108.2 93.8 --7.4 10% surfactant 133.0 95.0 35.7 Water 163.0 79.8 --23.7 20% surfactant 161.5 124.5 33.5 Water 197.0 163.5 -- 8.8 1 to 20% aqueous dispersions. Minus sign indicates weight loss. Table IV Water Retention of Callus Moieties Immersed in RO (CH2CH20),•SOaNa, or Water, and Dried Weight Change• (%) Drying Time 1 hour 24 hours 0.6% surfactant 42.9 1.4 Water 15.3 1.3 1.8% surfactant 10.0 -- 0.7 Water 7.6 2.8 6.0% surfactant 47.3 2.9 Water 32.3 1.9 12.0% surfactant 12.4 1.7 Water 3.1 2.1 Minus sign indicates weight loss. also increased. Moreover, while the experimental half generally picked up less water than the control, as shown in the 15-min drying time col- umn, it retained the water generally longer than the control. The results obtained with a sulfated ethoxylated long-chain alcohol are shown in Table IV. The concentrations tested ranged from 0.6 to 12%. It was found that, with these solutions, the water-absorption ca- pacity of the callus increased without the surfactant apparently being absorbed in the callus. These experiments with a few randomly selected surfactant solutions indicated that such solutions are able to modify water-retention capacity

146 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of stratum corneum that some solutions extract more solubles from skin than others and that there are variations in the amounts ot5 surfactant absorbed onto skin. Experiments with Soap The rate and amount of swelling of calluses was examined as a func- tion of concentration of toilet soap (Table V). The weight increases of callus halves at different immersion times were measured. The results indicated that throughout the concentration range of 0 to 2.4% soap solution, the callus immersed in soap solution absorbed more water than callus immersed in distilled water. These differences increased as either the soap concentration or the immersion time increased. The swelling did not increase linearly with the soap concentration or with the length of immersion. Table V Swelling of Callus Immersed in Soap Solutions of Various Concentrations and in Water Per Cent Swelling Soap concen- trations, % 0.6 1.2 1.7 2.4 Immersion 4.5 70 4 70 21 1.5 23 time, hours Soap solution 137.0 245.0 135.0 267.0 257.5 116.0 208.0 Water control 132.0 229.0 111.0 203.0 208.5 82.2 177.0 Difference 5.0 16.0 24.0 64.0 49.0 33.8 31.0 The weight increase of callus after immersion in aqueous solutions of a number of toilet soaps was examined. Bar A was a standard 85/15 tallow coco soap without additives Bars B to E represented commercial soaps with various "cosmetic"-type additives, such as mineral oil or cocoa butter Bars F, G, and H were deodorant soaps, while I and K were soap- synthetic combinations. Results obtained are shown in Fig. 4. It was found that in almost every instance soap enhanced the water uptake by stratum corneum. Pure soap base, A, in Fig. 4, had the highest swelling power of all the soaps we examined. Concurrent with water uptake during the immer- sion cycle, dehydration of hydrated callus was monitored (Table VI). The negative values may be due either to material leached out from the callus piece, or to superficial cells which desquamated.