SURFACTANT PENETRATION INTO HUMAN SKIN AND RESULTING SKIN DRYNESS 41 cup scrub collection takes less time in execution and analytical analysis. In the cup scrub collection procedure, there is only one sample to analyze, store, and document versus fi ve (or more) in tape stripping. In addition, tape strips require an extraction step, whereas the cup scrub sample can be processed as is, without any additional steps. Furthermore, tape strips must be extracted individually, as they stick together if placed in the same vial. In this study, it would have taken approximately 8 weeks to analyze 2,100 tape strip samples (70 subjects, six test sites/subject, and fi ve tape strips/site) versus 2 weeks to analyze 420 cup scrub samples (70 subjects, six test sites/subject, and one cup scrub sample/site) if all 15 formulations were tested. Cup scrub collection is also a less expensive procedure to perform, as the glass cups and stir rods can be cleaned and reused many times, whereas tape strips are consumable, expensive, and must be purchased for each use. In this study, the cost to complete the tape stripping procedure for 15 formulations would be $809 versus $187 for cup scrub collection. We, therefore, conclude that cup scrubs can be used for future surfactant skin penetration analysis, and may be the preferred method as they are less ex- pensive and require less time for collection and analytical analysis. If a depth profi le of surfactant penetration into the skin is desired, we recommend the use of tape strips. Tape strip and cup scrub analyses of varying surfactants revealed that total surfactant penetration into the skin as measured by either extraction method did not correlate well with 14 C-SDS skin penetration. However, when the surfactants were examined individu- ally, signifi cant trends emerged. We found some of the distributions of individual surfac- tants extracted from tape strips and cup scrubs to be positively skewed thus, medians are more representative for these data sets compared with means. On examination of correla- tions between tape strip and cup scrub extraction medians versus corneometer reading, visual dryness scores, and 14 C-SDS penetration means, we found similar or better R2 val- ues. However, because similar conclusions are found using the means, we chose to present the means here for consistency in understanding the error associated when comparing various measures. Skin penetration of SLE1S or 14 C-SDS, two anionic surfactants, seems to be a good predic- tor of clinical skin hydration state for anion-based systems. Penetration of CAPB, a zwit- terionic surfactant, can also be a good predictor of clinical hydration state for anion-based systems. The correlations between CAPB extractions and skin hydration measures lost signifi cance when the nonionic formulation was included. This may indicate that CAPB is not a good predictor of nonionic surfactant penetration, but CAPB penetration from F igure 1. Masses of individual surfactants extracted from either fi ve pooled tape strips or cup scrubs. Bars are stacked, and each bar represents the mean of 11–26 samples + SEM.

JOURNAL OF COSMETIC SCIENCE 42 F igure 2. SLE1S extracted from the skin using fi ve pooled tape strips or cup scrubs in vivo versus (A) corne- ometer CFB reading determined in vivo (B) visual dryness CFB scores determined in vivo and (C) 14 C-SDS skin penetration determined ex vivo. Data points represent mean ± SEM. ( ) Tape strip extraction (fi ve pooled extracts) ( ) cup scrub extraction.