The human body can't make Vitamin C
While most animals are able to synthesize vitamin C within their bodies, human beings must acquire vitamin C from external sources.
Journal of Cosmetic Dermatology, Volume 11 (4) – Dec 1, 2012, Stability, transdermal penetration, and cutaneous effects of ascorbic acid and its derivatives
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Liao, W. C., Huang, Y. T., Lu, L. P., & Huang, W. Y. (2018). Antioxidant Ability and Stability Studies of 3-O-Ethyl Ascorbic Acid, a Cosmetic Tyrosinase Inhibitor. Journal of cosmetic science, 69(4), 233–243.