Ulcerative colitis is an inflammation that occurs in the innermost lining
(mucosa) of the colon and/or rectum, affecting between 500,000 and 2,000,000
individuals in the United States, predominantly under age 30.8
Tiny open sores, or ulcers, form on the surface of the lining of the colon
and/or rectum, where they bleed and produce pus and mucus. The inflammation
usually begins in the rectum and lower colon, but may also involve the entire
colon.
When ulcerative colitis affects only the lowest part of the colon—the
rectum—it is called ulcerative proctitis. If the disease affects only the left
side of the colon, it is called limited or distal colitis. If it involves the
entire colon, it is termed pancolitis.