An anorectal abscess is a pocket of pus in the tissue near the end of the rectum (anus). Most abscesses are caused by a blocked anal gland that develops an infection.

Other possible causes of an anorectal abscess include:

• Infection in an anal fissure.
• Complications of diseases that affect the colon, such as Crohn's disease, inflammatory bowel disease, or diverticulitis.
• Sexually transmitted infections.

Symptoms of an anorectal abscess include:

• A painful swelling (mass) around the anus.
• Drainage of pus from the anus.
• Fever.
• Pain in or around the anus.
• Pain when passing stool.

A person should see a doctor if an anorectal abscess is suspected. Treatment is needed to prevent worsening of the infection and serious illness.