EFFECT OF COSMETIC EMULSIONS ON STRATUM CORNEUM 111 Water is continuously evapora- ting froIn the surface of the skin (5). This moisture stems from the tiny orifices of the eccrine glands and froIn the underlying tissues. The rate at which this moisture supply reaches the stratum cor- neum is controlled in a large meas- ure by a thin layer of tissue lying just beneath the stratum comeurn called the barrier layer (6). The stratum comeurn has a mesh-like structure made up of a mixture of 60 to 70 per cent of keratin and 30 to 40 per cent of water-soluble com- pounds (7). Normal stratum cor- neum contains 10 to 25 per cent water. Figure 2.--Desiccator fabricated from a glass cylinder, covered with polyethyl- ene snap cap. This water-holding ability of the stratum corneum is probably due primarily to these nonkeratinous, water-soluble, nitrogen-containing coinpounds (7, 8). Thus, a certain amount of the moisture reaching the stratum comeurn is retained by it and accounts for its flexibility and softness. However, it is entirely possible for the stratum comeurn to be deficient in the water binding components (9), in which case a dry scaly skin will result. And, of course, perfectly normal skin will lose moisture and become dry under conditions of low relative humidity (10). Figure 3.--Desiccator assembly showing cylinder, snap caps, gasket, elastic band and bandage clip.

112 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS By applying a layer of oil onto the stratum corneum, the rate of water evaporation from the surface of the skin may be reduced. This moisture, which normally would have been lost, is then deflected back into and increases the moisture content of the stratum comeurn, resulting in a softer skin. In an effort to study the effect of lotions on the water content of the ski% Powers and Fox (11) developed a method, using small desiccators, whereby the rate of moisture loss from the skin could be measured. The desiccator and assembly are shown in Figs. 2 and 3. In this test, the desiccators containing silica gel* are placed on the inner portion of the forearm and held in place by a strip of elastic pajama belting fastened with a bandage clip (see [Pig. 4). Using this test method, it was shown that water-insoluble oily materials definitely retard the percentage of moisture loss from the skin and that certain emulsifiers and humectants may actually accelerate this moisture loss. Data obtained with the ingredients tested are shown in Table 1. Further studies have revealed that the accuracy of the method may be improved by "calibrating" each subject. When the subject is quiescent, * "Tell-Tale" silica gel, 6-16 Mesh, Davison Chemical Co. Figure 4.--The desiccators in position on the inner surface of the forearm.