Black marks on both sides of the corners of the mouth may be caused by keratitis, long-term external use of drugs and other reasons. 1. Keratitis: Keratitis is related to bacterial infection, trauma, malnutrition and other factors, manifested in the corners of the mouth area of the skin erosion, scabs, pain and other symptoms, if not actively treated, the inflammation of repeated stimulation, may lead to the corners of the mouth on both sides of the phenomenon of the black marks. 2. long-term topical drugs: patients if the mouth long-term topical ointment, especially glucocorticoid ointment, may lead to the skin melanin deposits, there may be the use of medication parts of the skin atrophy, capillary dilatation and other manifestations. Black marks on both sides of the mouth may also have other causes, it is recommended to go to the hospital in a timely manner to improve the examination, to clarify the cause of the disease to give targeted treatment.