154 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS E•ect of Sebum on Water Vapor Transmission After the efficacy of the synthetic NMF was established, the effect of human sebum on the breathing of the skin was studied by measuring the insensible perspiration. For these studies the method of Gregory (18), which is basically an electrical hygrometer, was used. For the investigations described in this paper the following instrument was con- structed. Two copper electrodes were melted into the bottom of a glass beaker having a diameter of 3 cm. A cotton thread, 5 cm long, saturated with K C1, is wound around these electrodes in the form of a figure eight. This saturated thread serves as a semiconductor. The open end of this glass cell is padded with rubber so that the edge of the cell may be pressed air tight against the skin. The cell is connected to a LF 39 WTM* conductance meter. Absorption of moisture changes the resistance of the cotton thread, which is measured on the instrument. 0 2 4 6 B 10 12 14min Figure 2. Sum of five measurements with a cell on a phantom during 15 minutes temperature variations of water -- q-0.2øC Each cell is calibrated over a water surface serving as a model. As Fig. 2 shows, the deviations of one cell for five measuremen ts during 15 minutes and at temperature changes of the water of +0.2øC are relatively small. During these measurements it was proven that the galvanometer reading/time interval is the best usable measurement for the insensible perspiration. The resistance of the KC1 saturated cotton thread changes, depending on the presence of humidity in the cell, and is related to moisture uptake or moisture loss. The instrument also allows absolute measurements of the insensible perspiration. In this case the cell is calibrated as follows: The cell is connected with a flat cylindrical beaker having the same diameter as the cell. The beaker contains a weighed amount of water. After the galvanometer shows a certain reading, the beaker with water is removed * Wissenschaftlich-technische Werkstatte GMBH, Weilheim/Oberbayern, Germany.

COSMETIC FILMS ON THE SKIN 155 from the cell and weighed. In this way different galvanometer readings can be related to the amount of water taken up by the cell, and a calibra- tion curve can be prepared. From a calibration curve the water vapor given up into the cell by the insensible perspiration can be determined quantitatively. In the present investigation it was more important to determine the relation between the insensible perspiration and ex- ternal factors than to determine its absolute amount. Accordingly the amounts of water vapor given up by the skin were not determined in absolute figures but in relative ones. As the measurement of insensible perspiration readings of the galvanometer movement in given time intervals were used the results can be converted into absolute amounts by using a calibration curve for the cell. Before the start of the test the subject remains in the test room for at least 30 minutes to 1 hour. Normally the forearms are used as the test area. The subject sits in a comfortable chair in front of a table and places one forearm on the table with the inner side of the forearm facing up. It is very important to make sure that the test subject is always sitting in a comfortable position during the test. For each measurement the room temperature and the relative humidity of test room are re- corded. In many cases it is also important to determine the skin temperature of the adjacent skin. First, the insensible perspiration of the untreated skin is determined during 5-15 minutes. After constant values have been obtained, the material to be tested for porosity is applied to the skin area, and then the insensible perspiration is again determined. After this determina- tion, the material is removed by gentle wiping with cotton wool, and the insensible perspiration of the uncovered skin area is rechecked. To determine the porosity of a film on the skin surface for insensible perspiration, the insensible perspiration of the uncovered skin is taken as 100%. The insensible perspiration of the skin after application of the material to the skin is calculated as per cent of the water vapor release of the uncovered skin. Human sebum was collected from several test subjects by extracting their skin with ether and ethanol. RESULTS AND DISCUSSION Figure 1 represents the result of the analysis of the natural mois- turizing factor extracted from living human skin as determined by column and paper chromatography. Based on this analysis a NMF was synthesized. The ability of stratum corneum to pick up moisture