Anal swelling without other discomforts may be caused by prolonged squatting, rectal prolapse, ulcerative colitis, pelvic inflammatory disease, rectal cancer and so on. 1. Prolonged squatting: prolonged squatting may lead to increased burden on anal sphincter and cause anal distension, in addition to eating a lot of spicy and irritating food, frequent use of laxatives and other factors may also cause anal distension. 2. Rectal prolapse: when the mucosa of rectum prolapses out of the anus, it stimulates the dentate line and causes anal distension, which is often accompanied by symptoms of acute and severe pain and anal pain. 3. Ulcerative colitis: after the disease involves the rectum and sigmoid colon, the local intestinal mucosa will become ulcerated and oozing, which will cause anal distension, in addition, perianal abscess, anal papillitis and other inflammatory diseases may also cause anal distension. 4. Pelvic inflammatory disease: female patients with pelvic inflammatory lesions may involve the neighboring rectum, resulting in rectal mucosal irritation and anal distension. Ectopic pregnancy, cervical cancer, prostate hyperplasia and other diseases may also press and stimulate rectum and cause anal distension. 5. Rectal cancer: malignant hyperplasia of rectal mucosa leads to local occupation, bleeding, erosion and other changes, and stimulates the nerve fibers causing anal distension. There is nothing else for anal distension, it may be related to many factors, and the etiology is complicated. We suggest to consult the doctor as soon as possible, make a clear diagnosis, and give targeted treatment according to the doctor’s instruction.