Perianal abscess is accumulation of pus near the anus. It is usually a very painful condition causing a lot of discomfort while sitting. There are numerous glands lining the anal canal. These glands may get infected leading to an anal or perianal abscess.
Anal fissure (a tear in the lining of the anal canal) may get infected leading to an anal abscess.
Sexually transmitted infections in persons engaging in unprotected anal sex.
Blocked anal glands