346 JOURNAL OF COSMETIC SCIENCE Table II Stratum Corneum (S.C.) Cell Layers Corneocyte layers Treatment Mean baseline Mean 3 months Mean 6 months Product A 16.5 ñ 1.65 16.9 ñ 1.37 17.0 ñ 1.15 (8% GA) Product B 15.8 + 1.93 16.1 + 1.97 16.4 * 1.71 (4% GA) 25 • 20 w,,.._ •15 o ,... 10 o o • 5 Baseline I 12 weeks 1 24 weeks .. 01 02 03 04 05 06 07 08 09 10 Panelist identification # Figure 1. Cell layers of stratum corneum after twice-daily use of Product A for 12 and 24 weeks. Bars show corneocyte layers per person at each time point. DISCUSSION The absence of any sunburn cells in response to UVR challenge demonstrates that SPF 4 is sufficient to counteract any increase in sun sensitivity that might occur with AHA products. No data were collected earlier than six weeks, as earlier studies (15) indicated no effect of glycolic acid on sensitivity to one MED dose of UVR after short-term application (four days) at cosmetic product concentrations of glycolic acid (10%, pH 3.5), and showed a slight effect after 12 weeks of daily application. With one MED dose of UVR it is usual to detect a moderate number of sunburn cells (10). However, as previously reported, no sunburn cells were seen after six months of daily application of products containing 8% glycolic acid or 8% lactic acid (both at pH 3.8) and after everyday incidental exposure to UVR (11,12). In that study there were no sunscreens in the products. As regards safety after long-term use, we found that 8% glycolic acid at pH 3.8 did not produce any thinning of the stratum corneum. At the concentrations used in cosmetic

GLYCOLIC ACID IN SKIN CREAMS 347 25 t-'1 Baseline I 12 weeks 1 24 weeks r--1 01 o2 o9 10 03 04 05 06 07 08 Panelist identification # Figure 2. Cell layers of stratum corneum after twice-daily use of Product B for 12 and 24 weeks. Bars show corneocyte layers per person at each time point. 0.3 0.25 0.2 0.15 0.1 0.05 Product A Product B Figure 3. Quantitative analysis of D-Squames ©. Bars show group mean D-Squame values at each time point. 0 12 24 0 12 24 Weeks