Usually, bleeding moles on legs may be caused by trauma and melanoma. 1. Trauma: Bleeding may be caused by unintentionally touching sharp objects or blunt force injuring the skin of the leg. 2. Melanoma: a disease caused by excessive proliferation or malignant proliferation of melanocytes, which may be caused by genetic factors, gene mutation and other reasons. In the early stage, patients may have no obvious symptoms, and their skin may have black spots, or slightly elevated black papules. With the prolongation of time, the lesions may gradually expand, and the surface may become eroded and ulcerated, thus bleeding may occur. In addition, it is recommended to go to the hospital in time to see a bleeding nevus on the leg, do the relevant examination to clarify the cause of the disease, and then follow the doctor’s instructions for treatment to avoid delaying the condition.