Microscopic colitis is a disease that affects the large intestine, causing chronic diarrhea and abdominal pain. The inflammation and swelling of the colon tissue is only visible microscopically, hence the name microscopic colitis. It is related to Crohn's Disease and Ulceratic colitis. All share similar symptoms, but of these three, microscopic colitis is the only one not definitively linked to a increased rate of colon cancer.
There is no known cause of microscopic colitis, but some research suggests that it is a reaction of the immune system to the bacteria in the colon. Some studies have suggested a correlation between microscopic colitis and the use of NSAIDs (non-steroidal anti-inflammatory drugs), such as Advil.