Ulcerative colitis is a chronic disease of the colon, or large bowel. It causes inflammation and destruction of the tissue lining the colon.

What is going on in the body?

Ulcerative colitis occurs when the lining of the colon is attacked by the body's immune system. It involves an autoimmune response, which means that the person's body produces antibodies against its own tissues. The disease usually starts at the rectum and involves entire sections of the colon. The attack may cause abscesses, or pus pockets, in the lining.

What are the causes and risks of the disease?

The cause of ulcerative colitis is unknown. People with ulcerative colitis have an autoimmune response that destroys the colon lining. However, it is not known whether the response is the cause or the result of ulcerative colitis. Many scientists believe that the immune response is triggered by a virus or bacteria.

Stress and dietary factors do not cause ulcerative colitis. However, they may worsen the symptoms when someone has the disease. Spicy foods and dairy products may trigger symptoms, for example.