PREPRINTS OF THE 1996 ANNUAL SCIENTIFIC MEETING 245 at pH 3.0 remained unionized at pH 4.0, indicating that a decrease in penetration is likely for pH 4.0 formulations. Differential effects of pH on alpha-hydroxy acid-induced stimulation of epidermal desquamation and turnover DAVID THUESON, ELAINE CHAN, LAUREN OECHSLI, and GARY HAHN, Cosmederm Technologies Inc., La Jolla, CA 92037. INTRODUCTION The alpha-hydroxy acids (AHAs) can induce epidermal exfoliation. In addition, skin cell renewal induced by AHAs can reduce fine lines and wrinkles. The role of the concen- tration of specific acid(s) and pH of the product in producing these effects is contro- versial, but a lower (more acidic) pH and higher concentrations are purported to produce a faster onset of activity and to be more effective. We examined the effect on skin renewal rates of 10% lactic acid at a low pH (2.0), a moderate pH (3.0), and a high pH (4.0). METHODS The dansyl chloride labeling technique was used to measure stratum corneum renewal time. The stain was triturated at 5% (w/w) into white petrolatum, USP. A long wave ultraviolet lamp was used to visualize the stain. Baby Magic Baby Lotion & Aloe © (The Mennen Company) was used as the lotion vehicle. Lactic acid 10% was added to the lotion, and different samples were then partially neutralized using NaOH to adjust the pHs to 2.0, 3.0, and 4.0. The neet lotion vehicle (pH 4.0) served as the placebo control. SUBJECTS AND STRATUM CORNEUM STAINING WITH DANSYL CHLORIDE Nine female volunteers aged 29 to 52 years (mean 35 years) had two areas on the right and left volar forearms stained using Hill Top Chambers © (25-mm in diameter). After 24 hours, the patches were removed and the fluorescence was scored according to a subjective visual scale of 0-4 (0 = no fluoresence 1 = only small areas of fluorescence 2 = moderate areas of fluorescence with noticeable areas of fading 3 = large areas of fluorescence with small areas of fading present 4 = whole, even areas of fluorescence). INITIAL (ACUTE) TREATMENT--WEEKS 1-3 Subjects used three 1.5-ounce tubes of the 10% lactic acid lotions, one each at pH 2.0,

246 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS pH 3.0, and pH 4.0, a fourth containing the placebo. Coding of the tubes maintained the double-blind design. Right and left volar forearms sites were randomized. Subjects applied a V8th inch bead of the designated lotion to each site twice daily. Sites were examined on days 1 (baseline), 7, 9, 11, 14, 16, 18, and 21. The endpoint was designated as described below. PROLONGED (CHRONIC) TREATMENT--WEEKS 5-8 During weeks 3 to 5, subjects used each lotion twice daily after the initial stained spots disappeared. At the beginning of week 5, all four sites on the forearms of all subjects were restained with dansyl chloride and the subjects resumed lotion treatments twice daily to the same designated sites until the stain disappeared the second time. ENDPOINT AND DATA ANALYSIS Because the subjects returned only every second or third day (during weekends), the exact day of stain disappearance was estimated as follows: On the day of the visit when the dansyl stain was first gone, the previous visit day number of the last score was noted and then adjusted to the "disappearance day" by adding the value of the last fluorescence score (either a 1 or 2 or 3) to the visit day number. For example, if on day 13 the score was "1" and on day 15 "0," day 14 was designated the "disappearance day." RESULTS ACUTE TREATMENT--WEEKS 1-3 The mean time for disappearance of stain was calculated for the group for each of the four treatments. The means and standard error of the mean (x + SEM) for the acute treat- ment phase (weeks 1 to 3) are shown in Figure 1. All three lactic acid-containing lotions 21 19- 16. 1'7. •6. 14. 12 II 10 1•-4 tl.O pH 2.0 15.6 .* 0.8 15.4 • 0,8 i pH 3.0 pH 4.0 Treatment Figure 1. 18.1 ! !.6 I Placebo