The reason why the left leg is darker than the right leg is because of sun exposure and venous lesions. 1. Sun exposure: the left leg does not do sun protection measures, long-term exposure to sunlight, may lead to the left leg than the right leg color deep, such as the popular hole jeans, if the left leg is a large area of the hole, may lead to the left leg skin color deep. 2. Venous lesions: If the left leg thrombosed occlusive vasculitis, varicose veins in the left leg, etc. because of damage to the inner wall of the veins, local bruising to form erythema, reduced hemoglobin increases, resulting in deepening of the skin color of the left leg. Therefore, the left leg is darker than the right leg, patients should consult the doctor in time, clear causes, early treatment, do not be negligent, so as not to delay the condition.