There are two main possibilities: 1, hemorrhoids, is a common class of anorectal diseases, when its repeated prolapse outside the anus, can be the rectum of the liquid incidental to the perianal skin. Cause perianal skin moisture and chronic inflammatory changes, the phenomenon of wiping ass wipe not clean.2, anal fistula, mostly secondary to rectal perianal gap infection, including the internal mouth, external mouth and fistula, the typical clinical manifestations of the anus intermittent pus and fluid flow. When defecation can be part of the stool or intestinal lumen of the intestinal fluid through the inner mouth, flow through the sinus tract and finally discharged to the outside of the anus by the outer mouth. Therefore, when the phenomenon of wiping the buttocks can not be cleaned, you should go to the regular hospital anorectal surgery or general surgery, rectal fingerprinting or colonoscopy to make a clear diagnosis, and under the comprehensive assessment of specialists to decide whether to carry out surgical treatment.