344 JOURNAL OF COSMETIC SCIENCE We undertook to examine two leading glycolic acid creams for their effects on human skin over a 6-month period of twice-daily application. The specific aim was to evaluate possible adverse effects on the barrier properties of the stratum corneum. EXPERIMENTAL TEST PRODUCTS Two commercial AHA creams were examined. Both were creams with the same oil-in- water emulsion base, containing Glycolic acid pH SPF Cream A 8% 3.8 4* Cream B 4% 3.8 4* * From ethylhexyl-p-rnethoxy cinnarnate and oxybenzone. STUDY DESIGN The study was conducted in the Philadelphia area between January and July. Ten healthy women, of phototype I or II, applied product A to one volar forearm and product B to the opposite forearm twice daily for 24 weeks. The women were instructed to apply the products liberally. The approximate dosage was 3 mg/cm 2 per application. To ensure compliance and to detect any adverse effects, each subject was examined monthly by a dermatologist. The minimal erythemal dose (MED) was determined for each subject using solar- simulating radiation from a filtered 150-watt xenon arc lamp (Solar Ultraviolet Simu- lator Model 15S, Solar Light Co., Philadelphia, PA). At baseline, an MED dose was applied to the inner arm, with 3-mm biopsy 24 hours later. At weeks 6, 12, and 24 one MED was given to treated volar forearms. A 3-mm punch biopsy was taken 24 hours later, fixed in formaldehyde, and stained with haemotoxylin and eosin (H&E). The H&E sections were examined for sunburn cells (SBCs) (mean count per five high-power fields). In addition, cryostat-processed six-micron sections from shave biopsies were obtained at baseline and at 12 and 24 weeks. The cryostat sections were treated with 5% lactic acid to cause swelling of the corneocytes, enabling the number of cell layers to be determined. The procedure is essentially the same as described previously, using sodium hydroxide to cause swelling (7). A skin challenge with tetrahydrofurfuryl nicotinate (Trafuril) was conducted at baseline and at 12 and 24 weeks--this challenge provides an indirect measure of stratum cor- neum barrier integrity (8). Trafuril (1% tetrahydrofurfuryl nicotinate) was applied to treated sites for five minutes and then washed off. Laser-Doppler readings were made every two minutes until a peak reading was obtained, usually within a few minutes. A superficial corneocyte sample was obtained at baseline and at 12 and 24 weeks using D-Squame © adhesive tapes (9).

GLYCOLIC ACID IN SKIN CREAMS 345 RESULTS SUNBURN CELL FORMATION Histological evaluation of irradiated untreated skin sites showed the presence of SBCs in all but one subject (Table I). The number of SBCs was low and consistent with numbers published previously (10). In sites treated with test products for 6, 12, or 24 weeks, no SBCs were observed. STRATUM CORNEUM THICKNESS After six months of treatment with AHA products, the number of cell layers in the stratum corneum showed no significant change (Table II). Any trend in the data is in the direction of increased stratum corneum cell layers after six months of treatment with the AHA products (Figures 1, 2). D-SQUAME © EVALUATION D-Squame © samples provide an index of the looseness of corneocytes near the surface in readiness for desquamation. The greater the dryness the greater the number of squames that were removed. D-Squames were taken at baseline and at 12 and 24 weeks. The scale removed was quantified using an image analysis technique reported previously (9). There was a small reduction in readily removable squames after 12 and 24 weeks of treatment, with the effect somewhat greater for 8% glycolic acid (Figure 3). STRATUM CORNEUM BARRIER INTEGRITY There was no change in response to Trafuril challenge after 12 and 24 weeks of treatment with either product (Figure 4). Table I Sunburn Cells 24 Hours After One MED* Subject I.D. Baseline 6 Weeks 12 Weeks 24 Weeks 01 1.5 0 0 0 02 2.2 0 0 0 03 1.8 0 0 0 O4 3.2 0 0 0 O5 2.4 0 0 0 06 0.0 0 0 0 07 3.1 0 0 0 08 2.8 0 0 0 09 1.5 0 0 0 10 2.3 0 0 0 Mean 2.8 0 0 0 * Mean count per five high-power fields per subject.