Calf melanin precipitation may be caused by physiological factors such as ultraviolet radiation, but also may be caused by post-inflammatory hyperpigmentation, acanthosis nigricans and other diseases, which can be treated with general therapy and medication. 1. Physiological factors: If the calf is exposed to ultraviolet radiation for a long time, it may cause melanin precipitation, so pay attention to sunscreen in daily life, such as applying sunscreen, wearing long pants and so on. 2. Post-inflammatory hyperpigmentation: For calf melanin precipitation caused by post-inflammatory hyperpigmentation, patients can follow the doctor’s instructions for external use of azelaic acid, hydroquinone, tranexamic acid and other drugs to inhibit melanocyte proliferation. Vitamin A acid drugs have the effect of promoting epidermal renewal and reducing pigmentation, and it is recommended that patients use topical adapalene, tazarotene and other gels. 3. Acanthosis nigricans: For melanin deposits on the lower legs caused by acanthosis nigricans, patients can use topical retinoic acid gel, which can affect melanin production, but the drug has the risk of teratogenicity. Topical application of medium concentration keratolytic agents such as 10% sulfur coal tar ointment can also be used. There are many causes of calf melanin precipitation, after excluding physiological factors, it is recommended that the patient go to the hospital for consultation and standardized treatment after clarifying the disease.