ESCA STUDIES OF SKIN LIPID REMOVAL 293 Table V Surface Composition (wt. %) of the Skin after Treatment with Acetone or Ethanol for 47 and 37 Minutes Respectively Compared with That of Protein Element Average Protein Composition* Skin Composition (inner side) Washed with Acetone for 47 Min. Washed with Ethanol for 37 Min. C 59.9 63.8 62.2 O 23.0 21.6 22.7 N 17.1 14.6 15.0 * Taken from: General Biochemistry by Joseph S. Fruton and Sofia Simmonds (John Wiley & Sons, Inc., New York, 1959), p 27. With acetone or ethanol treatment, extraction of lipids from the skin increases with wash time as shown in Figures 2 and 3 and Tables III and IV. There is a difference in skin lipid removal from the two sides of the skin (Figures 2 and 3). Skin lipid removal is larger from the inner side as compared to the outer. After a 47-minute wash with acetone or a 37-minute wash with ethanol, the surface composition of the inner side approaches very close to an average protein composition as shown in Table V. Small amounts (• 1%) of sulfur, phosphorus, silicon and calcium were also observed at the surface of most of these skin samples. Silicon is maximal at the surface (--1-2 atomic %) and gradually decreases with depth. Sulfur is at a minimum at the surface (--0.2 atomic %) and increases with depth to a level of 0.5 atomic percent (after 27- ?$ $0 $VI $11 o -iTI / I I I I I I I I / / / - UNTREATED SKIN \ FOR 3'i' MIN. IN ETHANOL - I'J'S -174 -172 -I70 -161 -lit -1•4 -162 -144) BINDING ENERGY, (eV) Figure 4. Sulfur 2P spectra on untreated and ethanol-treated samples of skin.

294 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VI Variation in Outer Surface Composition of the Skin When Treated with Sodium Lauryl Sulfate (SLS) Elements (Atomic %) Treatment Time (Min.) C O N Si S 0 82.5 12.8 0.8 3.7 0.2 2 78.1 15.4 3.8 1.9 0.9 5 74.8 17.2 5.6 0.4 2.0 10 74.0 16.8 7.6 0.2 1.5 20 73.0 17.9 7.8 0.2 1.2 minute washes with acetone or ethanol). Sulfur at the surface is mainly in the form of S TM (sulfonate or sulfate), and after washing with ethanol or acetone for 17 minutes or more, sulfur exists in two distinct chemical forms the lower binding energy corresponds to disulfide sulfur, referred to as S-II, and the higher binding energy corresponds to sulfonate or sulfate and is referred to as S-VI. This is demonstrated in Figure 4 for the skin washed in ethanol for 37 minutes. The relative changes in the chemical form of sulfur with depth can be explained on the basis of the following: With extraction of lipid, particularly cholesterol sulfate (17), the S TM contribution to the sulfur peak de- creases. This removal of cholesterol sulfate increases the protein at the surface, and the contribution of S n increases. Secondly, the upper layers of the skin may contain S v• due to oxidation of the disulfide bond of the protein and, therefore, the ratio of SII/SVI increases with depth. Phosphorus exists in the form of phosphate and its percentage increases with wash time and reaches a maximum for the inner side (0.6 atomic %) after 17 minutes in ethanol. With further washing ( 17 minutes with ethanol), phosphorus content decreases. The same trend is observed with acetone washing, although the time frame is different. With acetone or ethanol washing, the outer side of the skin does not show a change in phosphorus content. It seems from the present study that solvent has to penetrate the skin surface to extract structural lipid. Penetration of the skin by solvent depends on the polarity of the solvent and the surface charge of the skin. Solubility parameters (which depend on the polarity of the solvent) of ether, acetone, and ethanol are 7.4, 10.0, and 12.7 respec- tively (18). A comparison of the skin lipid removal (Figures 2 & 3) with the solubility Table VII Variation in Outer Surface Composition of the Skin When Treated with Ethoxylated Alcohol Sulfate (AEOS-6.5 EO) Elements (Atomic %) Treatment Time (Min.) C O N Si S 0 81.0 14.3 0.7 3.9 0.2 2 77.5 16.9 3.8 1.1 0.6 5 77.1 17.7 3.9 0.6 0.7 10 75.2 19.1 4.1 0.7 0.9 20 72.5 21.9 4.1 0.5 1.2 30 70.4 22.0 6.0 0.4 1.1