The cause of ulcerative colitis (UC) is unknown, although experts agree that genetics play a major role as do some environmental factors. A theory suggests that an agent, possibly a virus or an atypical bacterium, interacts with the body's immune system to trigger an inflammatory reaction in the intestinal wall.
While much scientific evidence shows that people with UC have abnormalities of the immune system, physicians do not know whether these abnormalities are a cause or result of the disease. Physicians believe that there is little proof that UC is caused by emotional distress, however stress can make symptoms worse.
Although children and older people sometimes develop UC, it most often starts between the ages of 15 and 30. It affects males and females equally and appears to run in some families.