Anal fissures can become anal fistulas, especially recurrent fissures, which can form subcutaneous fistulas if they are not treated for a long time and become infected. There are other causes of anal fistula besides anal fissure, mainly including: 1, perianal abscess, if the abscess breaks down on its own after or after incision and drainage, it will form an anal fistula; 2, injury around the anorectum, such as trauma or anal thermometer, anoscopy, damage to the anal rectum, resulting in bacterial invasion, causing anal fistula; 3, surgery in the perineum, such as internal hemorrhoid injection or postpartum perineal suture Infection, which spreads to the anorectum and causes anal fistula; 4, tuberculosis, diabetes infection can also form an anal fistula afterwards.