A naturally-occurring crystalline organic acid found in many plants, including grapes and tamarinds. It is one of the chief acids in wine. Tartaric acid has antioxidant properties and is an alpha hydroxy acid, though it is not as well-researched when it comes to skin benefits as glycolic and lactic acids.
References for this information:
Human Metabolome Database: http://www.hmdb.ca/metabolites/HMDB00956