Common causes of black spots on the buttocks include coffee spots, Mongolian spots, seborrheic keratosis, congenital melanocytic nevi, and hyperpigmentation. 1. Coffee spot: the cause of this disease is unknown, may be related to blue light treatment, genetic factors and other factors, manifested as a round, oval or irregularly shaped spots. 2. Mongolian spots: Mongolian spots, also known as birthmarks, sacral spots or buttock spots, are a kind of birthmarks after birth, mainly due to the fact that during embryonic development, the melanocytes from the neural crest to the epidermis when the migration of the obstacles occur, and stay in the dermis, resulting in pigmentation. 3. Seborrheic keratosis: the etiology of this disease is unknown, may be related to skin aging, heredity, sun exposure, air pollution and other factors. 4. Congenital melanocytic nevus: the etiology of this disease is unknown, the skin lesions manifested as dark brown patches, uniform color, clear boundaries and other symptoms. 5. Hyperpigmentation:This disease can be caused by heredity, endocrine disorders, metabolic abnormalities, inflammation and other factors, manifested in the skin as black spots precipitation. It is recommended that patients go to the dermatology department of regular hospitals when necessary, under the guidance of specialists to clarify the diagnosis and rational treatment.