The left side of the anus is vaguely painful considering the following conditions: 1. It may be caused by a perianal abscess, which has inflammatory fluid inside the swelling caused by inflammation, leading to local pain and itchiness. The pain may be caused by hemorrhoids, which are usually caused by a lack of attention to diet, and may cause local pain, itchiness, redness and swelling during acute attacks, and may be accompanied by bleeding in the stool in severe cases. 3. The pain may be caused by inflammation of the perianal area. 5. It is not excluded that the pain is caused by anal fistula or anal fissure.