120 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table X Mean L* Values (S.D.) of Treated Sites in Test Cycle 2 During One Week of Daily Treatments, January-February 19907 Baseline Day I Day 2 Day 3 Day 4 Day 5 Final 66.85 66.29 65.52 62.40 • 60.32 • 56.52 •'• 57.96 z SLS (1.51) (1.72) (1.90) (2.31) (1.48) (1.77) (1.94) 65.11 65.70 65.04 64.79 64.73 65.49 65.32 SLES (1.50) (0.14) (1.91) (1.44) (1.69) (1.34) (1.31) Tallowate 65.34 65.91 65.91 66.25 65.80 65.86 65.76 (1.33) (0.94) (1.16) (0.94) (1.32) (1.01) (0.93) Each value is the mean of six subjects. Represents a significant difference at p = 0.05 level from the baseline value within each subgroup. Represents a significant difference at p = 0.05 level from the previous day within each subgroup. Figure 9. Relative change of brightness (treated vs. control-•cycle 1) during one week of daily treatments, October-November 1989. IMAGES OF SKIN REPLICAS AND IMAGE ANALYSIS Figures 11, 12, and 13 each show four images of skin replicas taken from the same patched site of a representative subject from each subgroup at pretest, day 3, day 5, and day 8. The progressive changes of the skin surface following repeated exposure to SLS are shown in Figure ! 1. Replicas of SLES and PEG-20 glyceryl monotallowate treatment sites are shown in Figures 12 and 13, respectively, which show only minimal changes.

CHANGES IN STRATUM CORNEUM 121 p 2-- Surfactan[ e r 0 c -! e -2 o SLS -3 n -4 a -6 g -7 e -B • SLES -9 c -tO h a -i2 g -t4-- 8 -t5 -- ,PEG20 I]a¾! Day2 Day:] Day4 I]a¾5 Fine! EvaIuaf. ton Figure lO. Relative change of brightness (treated vs. control•ycle 2) during one week of daily treat- ments, January-February 1990. For quantitative image analysis of the skin replicas, useful information was obtained on changes of the mean depth of the dermatoglyphics by calculating the mean ratio of the shadow areas to the shadow perimeters. Figures 14 and 15, respectively, show the mean ratios of all three subgroups at day 1 before exposure to surfactants and at day 5 after ten 45-minute patches in the two different test cycles. Significant changes between these two days were observed in the sites treated with SLS in both test cycles. No significance was calculated for the sites treated with either SLES or PEG-20 glyceryl monotallowate. DISCUSSION The daily treatments and measurements by a battery of instrumental, morphometric, and clinical methods demonstrated advantages over that of a single treatment and/or measurement procedure. The protocol of twice-daily patch applications for 45 minutes each provided the advantage of gradual skin changes in contrast to the effects obtained from a single 24-hour patch application. Together with the multiple measurements taken at daily intervals, important information was obtained with regard to the SC response to an irritant, which could be useful toward understanding the mechanisms of the induced changes. The consistency and the reproducibility of all measurement parameters were well dem- onstrated by the body of data obtained from both surfactant-treated and water-treated sites. The water-treated control sites showed no significant differences between day-