The main causes of anal fistula include the following: First, perirectal abscesses, which are the most common cause and account for over 95% of anal fistulas. Second, rectal and anal injuries caused by trauma, swallowing bones, metals, etc., lead to bacterial infection of the wound. Third, anal fissures, where recurrent infections can lead to subcutaneous fistulas. Fourth, perineal surgery, where incorrect injection into the base during internal hemorrhoid treatment or post-surgical infection can occur. Fifth, tuberculosis; many cases of tuberculosis include complications of tubercular anal fistulas. Sixth, ulcerative colitis, which can also lead to anal fistulas. Seventh, Crohn's disease, which is also complicated by anal fistulas.