The causes of anal darkening are often the following: a. Pigmentation: If the patient has long-term constipation or diarrhea, it will easily lead to local pigmentation. This is not too worried, usually actively adjust the diet structure can, try not to drink alcohol, do not eat spicy food, can be appropriate intake of fresh fruits and vegetables, appropriate increase water. Second, the anal infection: you can go to the hospital general surgery or anorectal surgery for clarification, if the problem, you need to give antibiotics for treatment, and at the same time can be combined with drug sitz bath treatment, sitz bath solution generally choose diluted warm potassium permanganate water or Chinese medicine preparations, etc., generally twice a day sitz bath, divided into morning and evening. Melanoma: If there is a sudden blackening and local breakdown, and does not love to heal, it may be caused by melanoma, need to go to the hospital surgery or dermatology as soon as possible to clarify.