SURFACTANT-SKIN INTERACTIONS 77 ß - T • ---• o-SLES-•oco • .... • .... SLES-oxo k. '• ................... • .... • .................................. ..•..: ...--:v.:::...-:=.:.•.. I I I I I I I I I I I 0.• 0.• 0,• 0.•0 0.• 0.•4 0.• 0.• 0.• 0.• s eurfactant Figure 4. Sur•ctant/liposome interactions--Response to changes in alkyl chains. 0,0 0,00 I I I I I I I I I ! I I O.Ol• 0.04 0.0• 0.0• O.l.O s eurfactant Figure 5. Surfactant/liposome interactions--Response to different anionic surfactant classes. = SLS .--O--SLES $ SLEC aggressiveness of a homologous series of straight-chain ethoxylated alcohols with iden- tical cetyl-stearyl alkyl chains bearing 10, 15, and 20 moles of ethoxylation respec- tively, i.e., with increasing hydrophile-lipophile balance. All three interacted extremely aggressively with liposomat membranes, and more so with increasing ethoxylation. In contrast with the above, an increase in the length of the polyoxyethylene chains has been

78 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS O.Ot 0.0• 0.0,.I 0.04 l{ SURFACTANT Figure 6. Modification of surfactant effect by ethoxylation of straight-chain C16/C18 alcohols. T C tO• ETHOXYLATION .... I .... tS• ETHOXYLATION •0• ETHOXYLAT[ON found to result in a decrease of surface activity for the nonionic polyoxyethylated t-octylphenols, i.e., Triton X100 (EO 9-10) and Triton X102 (EO 12-13) (Figure 7). Nonionic surfactants are used extensively in cosmetic formulations. Their effect on the skin appears complex and is not yet fully understood (22). With nonionic surfactants phospholipid liposomes interact generally strongly, resulting in increased membrane 8.0' 8.5' 8.0' 7.5' 7.0' 6.6' 5.5' 4.5' 4.0- 3.5' 3.0' 8.5' 8.0' 5..5- 1.o- 0,5' 0.0 0. oog 0.05.0 0.05.1 0.05.2 I 0.05.3 0.05.4 0.0i5 SURFACTANT I 0,05.6 I 0.05.7 I 0.05.8 I o.os.g I o. 080 Figure 7. Modification of surfactant effect by ethoxylation of polyoxyethylated t-octyl phenols. •--•9-i0% EO ......... i2-i3% EO