RANKING OF SURFACTANT-HUMECTANT SYSTEMS 603 (5,6,29). PBS in the donor compartments was then replaced separately with 1.5 ml of aqueous contacting solutions i-v (5 ,6,29), and left in contact with the SC of the p-FTS samples for five hours (6,29). Subsequently, aqueous contacting solutions i-v were removed and the donor compartments along with the p-FTS samples were rinsed four times with 2 ml of PBS to remove any trace chemical left on the skin surface and in the donor compartments. Subsequently, the p-FTS samples in the diffusion cells were ex­ posed to aqueous contacting solutions of 3 H-radiolabeled mannitol in PBS (1-10 µCi/ ml) for 24 hours (5 ,6). For additional experimental details, including a discussion of the liquid scintillation counting method used to determine the mannitol transdermal per­ meability, see references 5, 6, and 41. Skin electrical current and resistivity measurements. During each mannitol transdermal (skin) permeability experiment, two Ag/AgCl electrodes (E242, In Vivo Metrics, Healdsburg, CA) were placed in the donor and receiver compartments to measure the electrical current and the electrical resistivity across the p-FTS samples (5,6). A 100-m V AC voltage (RMS) at 10 Hz was generated by a signal generator (Hewlett-Packard, Atlanta, GA) and was applied across the two electrodes for 5 s. The electrical current across the skin was measured using an ammeter (Hewlett-Packard, Atlanta, GA). The electrical resistance of the p-FTS sample was then calculated from Ohm's law (5,6,41). The skin electrical resistivity was obtained by multiplying the actual skin electrical resistance by the skin area (A = 1.77 cm2) (5,6,41). Skin electrical current and resistivity measure­ ments were carried out before and during the permeation experiments at each prede­ termined sampling point. For each p-FTS sample, an average skin electrical resistivity was determined over the same time period for which the steady-state mannitol skin permeability, P, was calculated (5,6,41). IN VIVO SKIN BARRIER STUDIES The objective of this study was to conduct quantitative in vivo skin barrier perturbation measurements upon contacting volar forearm skin test sites of human volunteers with aqueous solutions i, ii, iv, and v. The control for these in vivo measurements was an untreated skin test site that was not occluded and that was not exposed to aqueous contacting solutions i-v. This control will be referred to hereafter as the in vivo control to differentiate it from the in vitro PBS control (iii). Note that this in vivo control was adopted because studies have shown that natural hydration of the skin in vivo can be mimicked in vitro by contacting skin with a PBS solution that has a pH of 7-7.4 (the in vitro control, which is similar to the in vivo pH of the hydrated SC (13-17)). The in vivo skin barrier perturbation studies were carried out using a modified soap chamber test (12,17 ,18). The modified soap chamber test involved application of patches con­ taining aqueous contacting solutions i, ii, iv, and v to skin test sites on the volar forearms of 96 female volunteers (four groups of 24). The volunteers were interviewed to verify that they had no known allergies to soaps or fragrances, and that they were not using any medications that could have interfered with the results of the study. 4 Following the enrollment of the volunteers, the condition of the skin barrier of the volar forearm test 4 Note that the equivalent in vitro selection criterion used was a skin electrical current 3 µA at the beginning of the study (6,41).

604 JOURNAL OF COSMETIC SCIENCE site was evaluated using various in vivo measurements (see the following three sections) at baseline (prior to treatment). Volunteers with TEWL values outside the normal range ( 10 g/m2hr) were excluded. Subsequently, the patch containing one of aqueous con­ tacting solutions i, ii, iv, or v was applied to the skin test site for five hours on Day 1. After approximately 18-20 hours on Day 2, the skin test site was re-evaluated. Some of the skin test sites were not exposed to the patches, and were left untreated and non-occluded to serve as the in vivo control (see above). The in vivo measurements were reported as deviations from the baseline measurements. Measurement of transepidermal water loss using an evaporimeter. Transepidermal water loss (TEWL) measurements provide a noninvasive instrumental assessment of the skin barrier function in vivo. Specifically, skin barrier perturbation may lead to a disruption of the intercellular lipid bilayers in the SC, thereby resulting in elevated water loss rates. Such elevated water loss rates can, in turn, lead to the skin becoming dry and chapped, thereby enhancing skin dryness (20-24). The TEWL measurements were made using an evaporimeter (CyberDERM, Inc., Broomall, PA) with probes manufactured by Cortex Technology (Hadsund, Denmark). This instrument is based on the vapor pressure gradient estimation method designed by Nilsson and initially utilized by the Servo Med Evaporimeter (25). The probes contain two sensors that measure the temperature and relative humidity at two fixed points along the axis normal to the skin surface. This arrangement is such that the device can electronically measure a value that corresponds to evaporative water loss from the skin surface expressed in g/m2hr. Additional details on the TEWL measurements using an evaporimeter can be found in references 26 and 27. The TEWL measurements were conducted following a 15-30-minute acclimation pe­ riod in a controlled environment, with the relative humidity maintained at less than 50% and the temperature maintained at 21 ° ± 1 °C. At baseline prior to treatment, TEWL measurements were conducted for each of the skin test sites. Any individuals .with TEWL values outside the normal range ( 10 g/m2hr) were excluded at this time. The test formulations were then applied to the test sites under occlusive soap chambers. On Day 2 (approximately 18-20 hours after patch removal), TEWL measurements were conducted for each of the skin test sites as described above. Evaluation of visual skin dryness by an expert grader. The visual skin dryness on the volar forearm test sites of each volunteer was evaluated by an expert grader using the grading scale described in Table I. Intermediate grades were allowed so that finer distinctions could be made. To conduct the study in an objective manner with no biases, the expert Table I Expert Grader Score System Used to Determine Visual Skin Dryness as Part of the In Vivo Soap Chamber Skin Barrier Measurements Grade 0 2 4 6 8 Description None Slight flaking/uplifting of flakes (patchy and/or powdered appearance) Moderate flaking/uplifting of flakes (uniform) and/or slight scaling Severe flaking/scaling, uplifting of scales and/or slight fissuring Severe scaling/uplifting of scales with severe fissuring/cracking