If there is anal swelling, the possible causes are as follows: First, rectal inflammation: inflammation of the rectum can be caused by ulcerative colitis, Crohn’s disease and other immune enteritis, may also be caused by bacterial infections, the most common is E. coli infection, and may also be caused by viral infections. Second, rectal mass: rectal mass can be benign or malignant lesions, accompanied by stool thinning and other related symptoms. Third, pelvic fluid: pelvic fluid can be gynecological inflammation, may also be more ascites combined with infection will appear anal swelling. If you find anal distension, it is recommended to go to regular specialized hospitals for systematic examination in order to make a clear diagnosis.