As of 2015, there is no scientific consensus as to the cause of ulcerative colitis, according to Mayo Clinic. Previously experts believed factors such as stress and diet caused colitis, but they now know these factors only aggravate the symptoms, and immune factors may play a role.
Researchers believe that several factors, including environment, genes and an overactive intestinal immune system, may cause ulcerative colitis, states the National Institute of Diabetes and Digestive and Kidney Diseases. However, these factors have not been proven as direct causes of the condition. Other factors such as diet and stress are now understood to cause flare-ups of colitis but not cause the condition itself.