A ten-millimeter black birthmark on the foreskin, usually present at birth, is a benign skin swelling that may affect aesthetics and increase psychological burden, but generally does not affect health. Some of them may also have adverse effects such as cancer. 1. Affecting aesthetics: Although the black birthmark grows on the foreskin and is relatively hidden, some patients or their sexual partners may find it unsightly. 2. Increase the psychological burden: many people will have a psychological burden due to the black birthmark on the foreskin and resist sexual behavior. Even anxiety, irritability, depression and other emotions. Currently need to have a correct understanding of the black birthmark, avoid excessive fear. 3. Cancer: congenital black birthmarks are usually benign lesions that do not affect health. However, if repeated stimulation and friction will also have the risk of cancer, so if the skin lesions expand, color change, etc., should consult a doctor in time to clarify the condition. Ten millimeters of black birthmark on the foreskin, it is recommended to consult a doctor in a timely manner, if necessary, for histopathological analysis, according to the diagnosis of the results of targeted treatment.