The presence of small black blood blisters at the scrotal tunica is considered to be due to scrotal trauma, scrotal angiokeratoma, benign capillary hemangioma, and scrotal eczema. 1. Scrotal trauma: There is a history of obvious scrotal trauma, which leads to rupture of capillaries on the surface of the scrotum and formation of small black blood blisters at the scrotal epidermis, with bruises inside the blisters. 2. Scrotal angiokeratoma: it is related to genetic factors of patients, mostly occurring in middle-aged and old men, which can lead to the formation of small black blood blisters on the surface skin of scrotum. 3. Benign capillary hemangioma: it belongs to congenital vascular malformation, when it occurs in the epidermis of the scrotum, part of it can be black small blood bubbles, the color can be faded by pressing, and it can be restored to black blood bubbles after loosening. 4. Scrotal eczema: it is mostly related to the humid and hot environment in the scrotum, and partly related to allergy. Papules and blisters can be formed at the scrotum, and some of them can be black.