If you want your anus to swell when you have a bowel movement, three times a day, it may be caused by sinusitis, hemorrhoids, and perianal abscesses. 1. If the sinuses due to bacterial infection and inflammatory lesions, the anus due to inflammation stimulation will appear swelling, pain, but also lead to perianal itching, defecation, urgency and heaviness (the lower abdomen is uncomfortable, want to relieve the stool, defecation after the feeling of incomplete) and other cases, cause to increase the frequency of defecation. 2. hemorrhoids is the anal canal skin under the venous plexus as well as the end of the rectum mucosa expansion and flexion of the vein mass, usually due to poor lifestyle and dietary habits induced, internal hemorrhoid prolapse embedded in the perianal area may lead to swelling and pain, but also caused by the defecation of laborious, rectal emptying incomplete, the number of times of defecation increased and other symptoms. 3. Perianal abscess is usually caused by infection of the anal crypt and obstruction of the anal glands. If the lesion location of perianal abscess is high, due to the accumulation of excessive pus in the pus cavity, resulting in excessive pressure in the pus cavity, there may be pus oozing, rupture of the pus cavity or inflammatory secretion so that the pelvic floor nerves that innervate the anal sphincter are stimulated. This leads to symptoms such as swelling and discomfort in the lower abdomen and anus, and increased frequency of defecation. In conclusion, if the above symptoms occur, you should go to the hospital in time to clarify the cause of the disease and give reasonable and standardized treatment as soon as possible to avoid delaying the condition.