What is Mandelic Acid? It is spoken of as a faithful ally of female beauty: mandelic acid. Similarly to malic acid, glycolic acid, and lactic acid, mandelic acid belongs to the category of alpha hydroxy acids, molecules widely used in cosmetics for the production of exfoliating, brightening, and antioxidant creams. Mandelic acid has made its way into cosmetics for about fifty years, immediately attracting the attention of many researchers; so much so that, even today, it remains a prestigious cosmetic ingredient used to brighten and exfoliate the skin.