There are many reasons for anal swelling and pain, such as anal fissure, hemorrhoids, perianal abscess and other diseases. 1. anal fissure: anal fissure can cause anal swelling pain unbearable, may be due to dry stool, defecation scratch perianal skin, thus causing anal fissure, especially in every defecation will have severe pain. 2. hemorrhoids: hemorrhoids can also cause swelling and pain in the anus, especially thrombosed external hemorrhoids with infection, will cause persistent severe pain. 3. perianal abscess: perianal abscess will also lead to the phenomenon of pain and swelling of the anus, at the same time will also be found in the perianal area there will be obvious lumps, hard to the touch or local fluctuation, the formation of abscesses, the need for timely incision and drainage. There are many other causes of anal swelling and pain, such as anal tumors, etc., after the symptoms need to go to the hospital in a timely manner to improve the examination, after a clear diagnosis to give standardized treatment, do not ignore the symptoms, take it lightly, so as not to delay the condition.