The cause of ulcerative colitis is unknown. People with this condition have problems with the immune system, but it is not clear whether immune problems cause this illness. Although stress and certain foods can trigger the symptoms, they do not cause ulcerative colitis. Ulcerative colitis may affect any age group, although there are peaks at ages 15 – 30 and then again at ages 50 – 70. The disease usually begins in the rectal area, and may involve the entire large intestine over time. Risk factors include a family history of ulcerative colitis, or Jewish ancestry.