352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 800- 800 400 go a'o INTERLAYER SPACING (•,) Figure 2. Comparison of x-ray diffraction spectra of washed and ether-extracted skin. /•, normal stratum corneum extracted for 30 minutes with ether ¸, washed normal stratum corneum O, region of complete spectral overlap. assigned with certainty. Tentatively, we interpret it as due to cavities formed in the structure by the extraction but are aware that other plausible explanations may exist. With this interpretation of the prominent feature of normal stratum corneum, the results are readily interpreted. First, washing of the separated stratum corneum removed epidermal lipids. From Figure 2, it can be seen that washing does not have as dramatic an effect on the stratum corneum as does extraction however, the effect on the 50- 80 • lipid region is virtually the same. The results gave essential information on the site of G2 in the stratum corneum. From the samples treated with G2 (Figure 3), it is evident that G2 interacts with and changes the structure of epidermal lipids. This is a relatively slow process continuing for several hours. Figure 3 reveals the trend of the change after one hour and also that the changes continue for a long time after that period. It is interesting to notice that the G2 dominated the spacings of the lipids. From earlier work on G2 (10), it was found that when G2 was added to a model skin-surface lipid mixture contained in a

STRATUM CORNEUM X-RAY DIFFRACTION 353 z LU I- Z LU LU 600- 400, a'o ' Jo ' 4'o 3'0 INTERLAYER SPACING (.•,) Figure 3. Effect of G2 with time on x-ray diffraction spectrum of skin. ¸, untreated normal stratum corneum [•, normal stratum corneum treated with G2 for one hour /•, normal stratum corneum treated with G2 for 13 hours O, regions of complete spectral overlap. lameliar liqu!d crystal, the G2 dominated the interlayer spacing, giving a characteristic value of 45 A. This effect was attributed to the ability of G2 to accomplish extremely good packing within the lameliar liquid crystal structure of a lipid mixture modeled exactly after the blend found in skin lipids (6,11, 12). 600 400 0ø% o o o o AA 0 øøOo A 0 A A 0 ! I 80 •'o 4:0 3'o INTERLAYER SPACING (•,) Figure 4. Effect of soybean oil on x-ray diffraction spectrum of skin. ¸, normal stratum corneum /•, normal stratum corneum treated for one hour with soybean oil O, region of complete spectral overlap.