Causes Make an Appointment Refer a Patient Ask a Question Reviewed by Miranda Y. Ku, MD, MPH (May 01, 2013) Crohn's Disease (CD) The cause of Crohn’s disease is not well understood. Diet and stress can make it worse, but are not necessarily the cause. Recent studies have suggested it can be genetic and/or environmental factors can play a role. The GI tract contains “good bacteria” that helps to keep your system balanced and helps with digestion. In people with IBD, these bacteria are recognized as foreign invaders, so the immune system attacks them. Cells migrate from the blood to the intestine and create inflammation. Inflammation is a normal response by your immune system, but in Crohn’s disease this inflammation does not go away, resulting in a chronic condition that will lead to developing symptoms of CD. Ulcerative Colitis (UC) In ulcerative colitis, the lining of the colon becomes inflamed and also develops tiny open sores, called ulcers. These ulcers produce pus and mucous. This can cause discomfort in the abdomen and frequent emptying of the colon. Just like with CD, the immune system attacks the contents in the intestine and creates the ulcers that produce the pus and mucous. Symptoms Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.