The phenomenon of melanosis of the skin on the legs is considered to be related to environmental factors and triggering factors. 1. Environmental factors: some patients may be due to long-term sun exposure, or because of the physical factors of heat stimulation radiation, which leads to the phenomenon of melanosis of the skin on the feet. In addition, when patients come into contact with photosensitizers, asphalt and other chemical stimuli, it may trigger photoallergic dermatitis, which may lead to the emergence of the disease. 2. Triggering factors: some patients may be due to skin trauma, wound in the process of healing, so that a series of inflammatory reactions, which will trigger post-inflammatory hyperpigmentation. Patients may also experience hyperpigmentation after mosquito bites or skin resurfacing. Whichever the cause of hyperpigmentation, most of them will subside on their own, generally do not need special treatment. Some patients may require photoelectric treatment, chemical peels, etc., which can help the pigmentation to reduce and fade.