The reasons for the darkening of the patient’s calf skin are considered as follows: 1, varicose veins of the lower extremities: mainly in people who stand and sit for a long time, due to the excessive pressure in the veins of the lower extremities, causing venous insufficiency of the lower extremities and the regurgitation and incomplete closure of the venous valves of the lower extremities, resulting in tortuous veins of the lower extremities, which can be seen on the skin protruding from the surface of the skin, like snakes. In the early stage, the skin color can be black, accompanied by itching, and in serious cases, there will be ulcers, so the treatment needs to go to vascular surgery. 2, sunburn: mainly due to long-term exposure to ultraviolet radiation, caused by the calf skin melanin particles deposited, the skin color is black, accompanied by itching, the treatment can choose tacrolimus ointment and urea vitamin E cream mixed with external use, and also oral compound glycopyrrolate. For black skin on the lower legs, it is recommended that patients go to a regular hospital and under the guidance of a doctor, undergo the appropriate laboratory tests to guide clinical treatment.