There are many common reasons for a small bump under the anus: first, if the swelling around the anus is hard in texture, the surface is cauliflower-shaped, bumpy, and sometimes there are mucus and other secretions leaking out, it may be anal canal cancer, which can generally be performed rectal finger diagnosis, and a biopsy can be taken for pathological examination to clarify the diagnosis. The second, the perianal warts, usually the condyloma acuminata, because the perianal viral infection and the perianal visible warts body, generally have a history of infection, local pathological examination can be performed to clarify the diagnosis. The third, hemorrhoids, such as long-term constipation sometimes makes the hemorrhoid nucleus stagnant, swollen so that the hemorrhoid vein stagnation, bleeding, hemorrhoid nucleus stagnant swollen so that the formation of hemorrhoids, manifested as a swelling around the anus visible.