Why does my anus bleed?

Many causes: A lot of reasons - some pretty bad, others not so much. You need a doc to examine you (you can't tell yourself - you need an exam). Not so bad: anal fissures, hemorrhoids, irritation. Need treatment: anorectal cancer, ulcerative colitis, chrohn disease. Occasionally bleeding can be from higher in the colon, or even small bowel or duodenum.

See doctor: Rectal bleeding is not normal and should always be evaluated. See a colorectal surgeon, who will do a complete evaluatin and examination, and can treat most causes of rectal bleeding.