Dioic Acid (Dicarboxylic acid) is an organic compound that is added to skincare products that for acne-prone skin, as well as products designed to reduce hyperpigmentation or ‘dark spots’ on skin. In acne formulas, it reduces the production of sebum and kills acne causing bacteria. In hyperpigmentation formulas, it regulates the production of melanin, which creates the pigment in skin.