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.

26 JOURNAL OF COSMETIC SCIENCE shows that the presence of glycolic acid significantly decreased the pH of all the der- mocosmetic bases studied. STUDY OF IN VIVO SKIN PENETRATION BY VITAMIN A PALMITATE IN THE FORMULATIONS UNDER STUDY After extracting vitamin A palmitate from the biopsy material, we determined its percentages of penetration as s function of time for the formulations studied. The results are presented in Table III. A test based on the Tukey test indicated that seven animals are sufficient to detect statistically significant differences for the variation determined by analysis of variance. ANALYSIS OF VARIANCE To determine the possible presence of statistically significant differences among the formulations studied in terms of vitamin A palmitate penetration into the skin, the data were analyzed by analysis of variance, followed by the Tukey test, which was more adequate for the mathematical model used in the experiment. The results are summa- rized in Tables IV through VII. Time factor, Analysis of variance revealed a significant difference at the 1% level with respect to the times studied in the present investigation, indicating that the time factor strongly affected vitamin A palmirate penetration into the guinea pig skin. The comple- mentary Tukey test for the time factor demonstrated that at time one-hour, penetration was significantly lower than at the other two times studied, which, in turn, did not differ from one another. The results of the Tukey test for the time factor are shown in Ta- ble IV. G/yco/ic acid factor. Analysis of variance showed that there was no significant difference in percent penetration between formulations containing or not containing glycolic acid. Table II pH Values Obtained Formulations pH Gel No additive Vitamin A palmitate added (2%) 70% glycolic acid added (10%) Vitamin A palmitate (2%) + 70% glycolic acid (10%) added Gel cream No additive Vitamin A palmirate added (2%) 70% glycolic acid added (10%) Vitamin A palmirate (2%) + 70% glycolic acid (10%) added Cream No additive Vitamin A palmitate added (2%) 70% glycolic acid added (10%) Vitamin A palmitate (2%) + 70% glycolic acid (10%) added 5.00 5.10 2.70 2.70 5.50 5.90 2.85 2.85 6.00 5.50 2.70 2.70