SURFACTANT SWELLING OF STRATUM CORNEUM 127 Table I List of Surfactants and Suppliers Surfactant Description and/ or Abbreviations Suppliers Alkylbenzene Sulfonates *Linear Alkyl (C•2 average) Benzene Sulfonate Alkyl Sulfates Alkyl Trimethylammonium bromides *Alkyl (C12-C14 average) Ethoxy Sulfates Paraffin Sulfonates Alpha Olefin Sulfonates Homologous series based on alkyl chain length LAS Homologous series based on alkyl chain length Homologous series based on alkyl chain length Homologous series based on average number of moles of ethylene oxide present, eg AEOS-3EO, AEOS-6EO, etc.* Homologous series based on an average alkyl chain length* Homologous series based on an average alkyl chain length* Coco Amidopropyl Betaine Betaine Lauryl Dimethyl Amino Oxide LDAO Magnesium Lauryl Sulfate - Triethanolammonium TEA lauryl sulfate Lauryl Sulfate Sodium Lauryl Sulfate SLS Dodecyl Trimethylammonium DTAB Bromide Tallow Soap - Tween 20 Nonionic Alfonic 1012 - 6 Nonionic Tergitol 25-L-7 Nonionic Conoco (Vista), Saddlebrook, NJ and Monsanto, St. Louis, MO Conoco (Vista), Saddlebrook, NJ Eastman Kodak, Rochester, NY and Sigma Chem. Co., St. Louis, MO Eastman Kodak, Rochester, NY and Sigma Chem. Co., St. Louis, MO Conoco (Vista), Saddlebrook, NJ Hoechst, Somerville, NJ Stepan, Northfield, IL Lonza, Fairlawn, NJ Onyx Chem. Co., Jersey City, NJ Henkel, Maplewood, NJ Henkel, Maplewood, NJ Sigma Chem. Co., St. Louis, MO Eastman Kodak, Rochester, NY Colgate-Palmolive, Piscataway NJ ICI, Wilmington, DE Conoco (Vista), Saddlebrook, NJ Union Carbide Co., Danbury, CT * Average means that in addition to the homologue specified, some species of the higher and lower homo- logues are present. RESULTS CONCENTRATION DEPENDENCE AND REVERSIBILITY OF STRATUM CORNEUM SWELLING Crosswise swelling of stratum corneum by SLS was assessed in response to concentration (Figure 1). The swelling response was concentration-dependent and appeared to saturate

128 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS r L'-,' lhr SLS Concentration (mM) Figure 1. Concentration-dependence of the swelling response of human stratum corneum to SLS. Time periods shown are incubation times after which readings were taken for the various doses. Swelling values are percent increases from hydrated lengths. Arrow denotes the critical micelie concentration (CMC) of SLS. at approximately 8 mM SLS this is also the critical micelie concentration for SLS. Swelling increased with longer exposure times, confirming previous results (2). In a separate study, we examined the effects of higher concentrations of SLS and other surfactants (Figure 2) on stratum corneum swelling. It is important to note at this point that due to large biological variation between individuals, we cannot compare, with confidence, data from one figure or table to another because the data were obtained in separate experiments. Results for the highest concentration of SLS studied (175 mM) showed a significant decrease from the swelling value at the preceding concentration (80 mM). This swelling decrease was also found for LAS, AEOS-3EO, and DTAB. The