VITAMIN A AND LIPOIC ACID STABILITY 413 Figure 7. Percentage of vitamin A palmitate vs time in system D. Figure 8. Percentage of lipoic acid vs time in system A. over time of vitamin A palmitate, suggesting that degradation has oxygen as a photodeg- radation partner. Based on experimental results, we concluded that although lipoic acid in not very stable, the presence of vitamin A and a higher pH favors its chemical stability. Thus, a determining factor in the preformulation of semi-solid mixtures with vitamin A and lipoic acid is the necessary control of the system’s stability against oxidation.

JOURNAL OF COSMETIC SCIENCE 414 Figure 9. Percentage of lipoic acid vs time in system C. Figure 10. Percentage of lipoic acid vs time in system D. ACKNOWLEDGMENTS This work was supported by grant B072 to A. I. Segall from UBA. REFERENCES (1) H. Beitne, Randomized, placebo-controlled, double blind study on the clinical effi cacy of a cream con- taining 5% α-lipoic acid related to photoageing of facial skin, Br. J. Dermatol., 149, 841–849 (2003).

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