SURFACTANT-SKIN INTERACTIONS 313 lOO = 90 • 80 Z •. 7o 60 0 ß 7 •J SDS • HMSC, Laurate / SLI • _ o_. -- / 20 Water o r : lactan i,inling• ,. ,url./,n. ii& • 2 0.1 0.2 0.3 0.4 0.5 0.6 Binding, mg SurfactanUmg Corneum Figure 8. Correlation of ANS displacement from stratum corneum by pure surfactants with their binding. Inset: results for 1-min equilibration time. 0.05 0.5 I ß ß 0.2 • 0.1 •, 0.02 0.01 0.005 0.002 0.001 SLS 1 hr 1 SLI 1 hr SLS 2 min. [] [] SLI 2min 0 20 40 60 80 100 120 Free Surfactant Concentration, mM Figure 9. Influence of equilibration time on the binding of pure anionic surfactants to porcine stratum corneum surfactant. the bar and the anionic probe ANS are either directly competing for the same binding sites in corneum proteins or that there is a significant overlap between the binding sites such that the electrostatic repulsion between the two negatively charged ligands be-

314 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1.0 0.8 0.6 0.4 Human Stratum Comeurn 1 min. treatment @37qZ 10% product dispersion -r -- :- _ _ __ 0.2 0.0 Water Bar A Bar B Bar C Figure 10. Displacement of ANS from isolated human stratum comeurn treated with water and with 10 wt% aqueous slurries of personal washing bars: l-rain treatment followed by 30-sec rinse • 37øC. comes important. The recovery of tryptophan emission after product treatment excludes the possibility that the loss of ANS fluorescence might be due to energy transfer from ANS to surfactants bound to a different distant site at the same molecule. INTERACTIONS OF DERMATOMED SKIN WITH CLEANSING PRODUCTS Experiments with dermatomed porcine skin were carried out to stimulate the interac- tions of skin with a cleanser during a wash. In these studies, the epidermal side of dermatomed skin was sprayed with ANS in an ethanol solution. After drying and equilibration, it was contacted with 1% product dispersion for one minute at 37øC. The ANS fluoresced intensely with an emission maximum of around 465 nm. Tape stripping with "Cellotape" (Hadleigh Enterprises Ltd., Essex, U.K.) of dermatomed piglet skin was performed to locate the ANS penetration depth. No fluorescence from ANS could be detected after five tape strippings of the skin. The results indicate that ANS was bound to the corneum proteins and did not penetrate into the viable epidermis to any appreciable degree.