24 JOURNAL OF COSMETIC SCIENCE pollution) and indicates its use in after-sun products because of its "normalizing" (corrective) properties (9-12). Alpha-hydroxy acids, and glycolic acid in particular, are currently being used as actives to treat signs of skin aging (13,14). Glycolic acid at low concentrations in combination with dermocosmetic formulations containing vitamin A palmitate has been prescribed by many dermatologists, who believe that glycolic acid, by stimulating natural skin desquamation and increasing skin hydration, may promote a better bioavailability of vitamin A palmitate in the skin. This theory, however, is based only on clinical obser- vations. The objective of the present investigation was to study the effect of glycolic acid on in vivo skin penetration by vitamin A palmkate in gel, gel cream, and cream formulations containing vitamin A palmkate combined or not combined with glycolic acid. EXPERIMENTAL PROCEDURE SAMPLES OF COSMETIC PREPARATIONS Three formulations (Table I) were prepared in a Fisatom shaker at approximately 2000 rpm and supplemented or not supplemented with 2% vitamin A palmitate (1,000,000 IU/g) combined or not combined with 10% glycolic acid at 70% concentration. pH DETERMINATION The pH of the formulations under study was measured with an Analion pH-meter using samples diluted 0.5:10 in distilled water. STUDY OF IN VIVO SKIN PENETRATION BY VITAMIN A PALMITATE IN THE FORMULATIONS UNDER STUDY To assess in vivo penetration we used 24 guinea pigs weighing on average 350 g. The animals' backs were depilated, and 0.05 g of the formulations listed in Table I supple- Table I Formulations Percentage of components in each formulation Components F1 F2 F3 Hydroxyethyl cellulose 2.00 2.00 -- Glycerin 3.00 3.00 3.00 Propyleneglycol 2.00 2.00 2.00 Methyldibromo glutaronitrile and phenoxyethanol 0.20 0.20 0.20 DL-o•-tocopherol 0.01 0.01 0.01 Squalene -- 2.00 2.00 Hydrogenated lecithin (powder) -- 1.00 1.00 Self-emulsifying base -- 4.00 Distilled water q.s. 1.00 1.00 1.00

GLYCOLIC ACID AND SKIN PENETRATION 25 mented with vitamin A palmitate and with vitamin A palmitate plus glycolic acid was added to paired areas of 2.0 cm 2 each. The formulations containing vitamin A palmitate were added to one of the paired areas, and the formulations containing vitamin A palmitate plus glycolic acid were added to the other. After observation for one, two, and four hours, the skin surface of the animals was cleaned with ethyl alcohol and biopsies were obtained with the aid of a dermatologic punch, with the removal of a 0.5 cm 2 area, as illustrated in Figure 1. The biopsy material was fragmented with a forceps and surgical scissors and extracted with isopropylic alcohol for 24 minutes by ultrasound. After extraction, the material was filtered through a qualitative paper filter, the flitrate was made up to a defined volume, and samples of the flitrate were concentrated and submitted to spectrophotometry using a double-beam Beckman spectrophotometer at 326 nm. The amount of vitamin A palmitate that penetrated the skin was calculated using a standard vitamin A palmitate curve, as shown in equation 1' A/A• x 100 = % vitamin A palmitate present in the skin (1) where A is the amount of vitamin A palmitate at one, two, or four hours, and A• is the amount of vitamin A palmitate applied to the skin. RESULTS DETERMINATION OF THE pH OF THE FORMULATIONS UNDER STUDY The pH values obtained for the formulations under study are listed in Table II, which Formulation containing vitamin A palmitate (2%) Formulation containing vitamin A palmitate (2%) i and glycolic acid (10%) 1 hour: O.05g of the formulation t•...i... '•':5-•• 2 hours: O.05g of the form "• 4 hours: O.05g of the formul Where: '"•::•0 = aplication area: 2.0 cm 2 '0 = biopsie area: 0.5 cm 2 Figure 1 Schematic representation of the skin of the guinea pig dorsum with the areas used in the study of vitamin A palmitate penetration.