We have already described the small crypts, or little glands, in the lining of the anal canal which secrete oil. The high pressure from straining forces the stool into the crypts. Feces trapped in these little crypts can fester and cause infections, abscesses and fistulas. Abscesses are pockets of pus within the flesh. Abscesses can cause fistulas.
Fistulas are tunnels through the flesh from the anal canal to the skin.
Fistulas can cause chronic discharge or drainage. The abscesses are extremely painful, swollen and tender. Abscesses should be treated as soon as possible so that they do not damage the anal sphincter muscles. Antibiotics alone usually do not help, because antibiotics cannot get into the abscess cavity which is filled with pus. Surgery is required to drain abscesses.