We have 8 to 10 of small glands around our anus, helping to ease the passage of fecal matter through mucus secretion. They can become blocked with bacteria or fecal matter. Once blocked, they may become infected. They then fill with pus. An anal abscess is a painful condition in which a collection of pus develops near the anus. The anal glands are located in the intersphincteric space (between the internal and external anal sphincters); therefore infection from the glands here spreads to adjacent areas.
Anorectal abscesses are thus categorized by the area, in which they occur: (1) Perianal (2) Ischiorectal (3) Intersphincteric (4) Supralevator. The most common type of abscess is a perianal abscess. About 50% of patients with an anal abscess will develop a complication called a fistula.