Component of grains such as wheat, rye, and barley, azelaic acid is effective for a number of skin concerns when applied topically, including skin brightening.
Azelaic acid is also an antioxidant, and has pronounced skin-soothing effects.
References for this information:
Journal of Cosmetic Dermatology, September 2016, issue 3, pages 269-282
Skin Therapy Letter, January 2016, issue 1, pages 1-7
Cutis, January 2016, issue 1, pages E9-E11
Journal of Drugs in Dermatology, September 2015, issue 9, pages 964-968