Diverticular diseases involve small pouches, called diverticula, that form in weak spots of the colon wall—most often in the lower (sigmoid) colon. Diverticulosis means these pouches are present; many people have no symptoms. Diverticular disease is the term used when diverticula cause chronic symptoms, bleeding, or inflammation.
Diverticulitis is inflammation of one or more pouches and can cause sudden abdominal pain, fever, nausea, or changes in bowel habits. Diverticulosis becomes more common with age: more than 30% of U.S. adults ages 50–59 and more than 70% of those older than 80 have diverticulosis, while fewer than 5% of people with diverticulosis develop diverticulitis.