Table II Results from the FCAT and 14 C-SDS Skin Penetration Studies Measurement Code A B C D E F G Corneometer reading,CFB a –13.09 –8.48 –10.92 -8.89 -8.10 -11.58 -5.16 Visual dryness score,CFB b 1.489 1.082 1.164 1.064 0.911 1.365 0.736 Tape strip extract (fi ve pooled extracts),μg c SLE1S 48.4 ± 6.6 29.9 ± 3.6 30.5 ± 4.5 15.0 ± 2.0 17.8 ± 3.8 49.9 ± 7.1 – CAPB 23.8 ± 3.3 40.3 ± 5.5 – – – 22.9 ± 3.2 7.8 ± 1.4 SCG – – 55.5 ± 8.8 – – – – NaLAA – – – 11.1 ± 1.7 11.8 ± 3.2 – – EcoSense – – – – – – 25.5 ± 3.2 Cup scrub extract,μg c SLE1S 79.5 ± 7.3 45.5 ± 4.2 71.6 ± 14.1 37.1 ± 4.1 30.8 ± 3.5 87.4 ± 9.5 – CAPB 51.7 ± 5.3 83.9 ± 9.5 – – – 55.8 ± 7.2 15.9 ± 2.1 SCG – – 65.7 ± 12.9 – – – – NaLAA – – – 28.9 ± 3.9 28.6 ± 3.9 – – EcoSense – – – – – – 71.3 ± 9.8 14 C-SDS penetration into and through the skin,% d applied radioactive dose 0.247 ± 0.044 0.106 ± 0.018 0.198 ± 0.035 0.175 ± 0.030 0.087 ± 0.015 0.277 ± 0.048 0.095 ± 0.016 a Adjusted mean CFB pooled SEM = 0.35, n = 22–24. b Adjusted mean CFB pooled SEM = 0.055, n = 22–24. c Arithmetic mean ± SEM, n = 11–26. d Geometric mean ± SEM, n = 12–14. SURFACTANT PENETRATION INTO HUMAN SKIN AND RESULTING SKIN DRYNESS 39

JOURNAL OF COSMETIC SCIENCE 40 penetration into the skin as measured by tape stripping in vivo was found to correlate well with 14 C-SDS skin penetration ex vivo (R2 = 0.996, p 0.05). Interestingly, comparison of Figures 2 and 3 reveals that SLE1S and CAPB penetration into the skin from anion- based formulations has opposite relationships with the in vivo skin hydration mea- sures and with the ex vivo skin penetration measure. For example, higher corneometer readings are associated with decreased SLE1S skin penetration and increased CAPB skin penetration. DISCUSSION The test cleansers examined in this study were formulated using strategies to maintain optimum skin hydration while still providing lather and adequate cleansing effi cacy for rinse-off applications. Although none of these strategies completely offset the skin dry- ness induced by multiple daily exposures to the test formulations over a period of 5 d in the FCAT study, some formulations were able to mitigate adverse effects in a reproducible manner better than others. 14 C-SDS skin penetration ex vivo was found to be a good pre- dictor of clinical skin hydration as quantitated with corneometer and visual dryness scores in the FCAT study. A 5-h exposure of pig skin to surfactant solutions containing 14 C-SDS used in Blankschtein et al. (11) and subsequent publications has been replaced by a 2-min exposure on human skin in this study (15). The changes not only involve exposures more consistent with consumer use of rinse-off products, but they also avoid making inferences about human exposure from pig skin, which has a different array of skin appendages than human skin (17–21). Penetration pathways for polar or amphiphilic compounds are not completely understood and may be different in porcine and human skin. The results of this study show that 14 C-SDS skin penetration may be a useful preclinical test for mild- ness of rinse-off products containing anionic surfactants. Cup scrubs consistently extracted more material than did fi ve pooled tape strips. This may simply be because surfactants are more readily extractable using liquid than tapes. The extraction liquid likely solubilized surfactant molecules that were loosely bound to proteins and those within stratum corneum (SC) lipid layers deep in the skin compared with tape strips, which only remove one SC layer at a time. In execution, the tape strip sampling procedure is easier to perform than the cup scrub collection. The cup scrub col- lection requires the technician to hold the cup in place with enough pressure to ensure a good seal to prevent the solution from leaking out of the cup. The potential for leakage can compromise the sample and provide opportunity for experimental error. However, Tabl e III Ratio of Surfactant Mass Extracted by Five Pooled Tape Strips to Surfactant Mass Extracted by Cup Scrubs Surfactant extracted Tape strips/cup scrubs (%) SLE1S 58.8 CAPB 41.4 SCG 40.0 NaLAA 40.0 EcoSense 40.0 Total 48.9