Ulcerative colitis (UC) is a chronic disease in which the lining of the large intestine (colon) becomes inflamed.
The colon then develops ulcers (open sores) that produce blood, pus, and mucus.
The small intestine is rarely affected.
The combination of inflammation and ulcers often causes abdominal discomfort, frequent bowel movements, and bloody stools.
Ulcerative colitis is a type of inflammatory bowel disease (IBD), but it's not the same as irritable bowel syndrome (IBS).
Although the disorders share some of the same symptoms, such as abdominal pain and diarrhea, inflammation or ulcers do not occur with IBS.