138 JOURNAL OF COSMETIC SCIENCE A. SALICYLIC ACID 0.4 Li .1 0.0 0 2 4 6 8 10 Time (Hours) B. LACTIC ACID 2.0 0 5 10 15 20 25 30 Time (Hours) Figure 1. Effect of PP-15 on the permeation of salicylic acid and lactic acid through pig skin. A: ¸, Control •, 0.3% PP-15' ', 1% PP-15 O, 3% PP-15 ', 6% PP-15. B: C), Control O, 3% PP-15. EFFECT OF PP-15 ON THE UPTAKE OF SALICYLIC ACID AND LACTIC ACID IN PIG SKIN The distribution of SA (0.5 % w/w) in the SC and the viable skin over time are presented in Figures 2A and 2B, respectively. The levels of SA recovered in the SC were highest at the two-hour time point then decreased over time. A trend can be noticed in Figure 2A where the presence of the polymer increased the levels of SA in the SC. A statistical significance was obtained only at the four-hour time-point (Figure 2A) when each time point was evaluated independently. When the overall amount of SA deposited in the SC was evaluated, a significant increase in SA deposition was obtained in the presence of the polymer. The polymer did not change significantly the levels of SA in the viable skin (Figure 2B). The levels of SA in the viable skin were highest at the two-hour time point, and then decreased steadily over time. This behavior corresponded to the pattern ob- served for the flux values of SA through the skin from the same formulations.

POLYETHYLENE GLYCOL-8/SMDI COPOLYMER 139 A. STRATUM CORNEUM 0.032 ,•, 0.024 o 0.016 r.• 0.008 0.000 2 3 4 5 6 7 8 Time (Hours) B. VIABLE SKIN 0.032 0.024 0.016 0.008 0.000 2 3 4 5 6 7 8 9 Time (Hours) Figure 2. Effect of PP-15 on the levels of salicylic acid in the stratum corneum and the viable skin over time. A: ¸, Control O, 3% PP-15. * Indicates a statistically significant difference between the two values at the same time-point. B: ¸, Control O, 3% PP-15. The distribution of LA (5.0% w/w) in the SC and the viable skin over time are presented in Figures 3A and 3B, respectively. The presence of the polymer did not affect signifi- cantly the levels of LA in the SC. The polymer lowered the levels of LA significantly in the viable skin at the 20-hour time point. No statistical difference was noted at the three earlier time points. EFFECT OF PP-15 ON THE PERMEATION OF SA FROM SUBSATURATED AND SATURATED FORMULATIONS THROUGH PIG SKIN Three levels of SA were studied, namely, 0.1%, 0.5%, and 2.0% w/w. Formulations