There is no possibility of self-healing once the anal fistula is formed for the following main reasons: 1. The anal part cannot be sedated: the abscess cavity is not easily bonded, and the anal sphincter is often in spasm due to contraction of the sphincter or due to inflammation stimulating the anal sphincter when defecating or urinating. 2, the presence of the internal mouth: although the abscess breaks down or has been incised and drained, the primary source of infection such as anal sinusitis, or anal gland infection still exists, and the contents of the intestinal cavity can also continue to enter the fistula through the internal mouth. 3, the lumen is difficult to close: feces, intestinal fluid and gas in the intestinal cavity continue to enter the fistula, stimulating the wall of the tube, so that the wall of the connective tissue thickening, the lumen is difficult to close. 4, poor drainage: the tube more than at different heights through the anal sphincter, sphincter contraction impede the discharge of pus, resulting in poor drainage. 5, easy to appear new fistula: poor drainage of the abscess cavity, or narrowing of the external mouth, sometimes closed and sometimes collapsed, pus accumulation in the cavity, resulting in abscess re-emergence and penetration and the formation of a new branch or fistula.