The possible reasons for the appearance of black patches on the body include sunburn, post-inflammatory hyperpigmentation, seborrheic keratosis, acanthosis nigricans and so on. 1. Sunburn: prolonged exposure to sunlight will cause local skin to be damaged by excessive ultraviolet light, resulting in localized sunburn, resulting in melanin spots and plaques on the body, which can be accompanied by different degrees of burning sensation of the skin, pain and other symptoms. 2. Post-inflammatory hyperpigmentation: If the phenomenon of black patches on the body before the patient himself there are skin allergies, breakouts, trauma, inflammation and other diseases of poor healing, then the body of the black patches may be caused by post-inflammatory hyperpigmentation, this kind of patients generally do not need to be treated, and with the prolongation of time, hyperpigmentation can be slowly faded. 3. Seborrheic keratosis: ultraviolet radiation, skin aging, viral infections can cause seborrheic keratosis, which is mainly manifested as round or ovoid papules or plaques, light brown to black, clear boundaries, the surface can be accompanied by varying degrees of roughness and thickening, especially in the trunk and the head and face, therefore, the black patches on the body may be seborrheic keratosis. 4. Acanthosis nigricans: Acanthosis nigricans may also cause the occurrence of black plaques on the body, which mainly occurs in the armpit, neck and other parts of the body, in addition to the local skin color deepening can also be accompanied by papillary or velvety thickening of the skin, which is characterized by certain features. There may be other reasons for the appearance of black patches on the body, it is recommended that patients with black patches on the body go to the hospital to clarify the cause of the disease, timely treatment, to avoid further aggravation of the condition.