New discoveries of the action of L-ascorbic acid (vitamin C) - Enhanced efficacy in formulations

Skin oxidation can impair physiological functions and induce skin diseases, such as photoaging and cancer. L-ascorbic acid (L-AA), or vitamin C, is commonly used in cosmetics because it is a potent antioxidant, inhibits melanogenesis, and promotes collagen and elastin synthesis in the skin. This study developed strategies to improve the stability of L-AA in its pure form with or without caffeic acid (CA) and evaluated its clinical efficacy using an ex vivo method. Oil/water emulsions were prepared with antioxidants and normal stability tests were conducted (various temperatures for 360 days). Antioxidant activity was assessed using a DPPH assay, and L-AA content was quantified by high-performance liquid chromatography. The thiobarbituric acid reactive substances method characterized the inhibition of lipid peroxides in the stratum corneum ex vivo. The formulation F1 (base + 10.0% L-AA) exhibited better L-AA stability over 360 days. The formulations F1 and F2 (base + 10.0% L-AA + 0.2% CA) increased the production of lipid peroxides when applied to the stratum corneum ex vivo and irradiated; however, when not irradiated, they inhibited the production of reactive oxygen species. For greater clinical efficacy of vitamin C on the skin, nighttime use is suggested as well as storage at low temperatures.