Diverticulosis refers to the presence of small, bulging pouches called diverticula that form in the lining of the colon, especially in the sigmoid colon. These pouches develop when weak spots in the colon wall allow the inner layer to push through. Diverticulosis is common, particularly among older adults, and often causes no symptoms. It’s typically discovered during tests like a colonoscopy. Diverticulitis, however, occurs when these pouches become inflamed or infected. This can happen when bacteria are trapped in the diverticula, leading to infection. Symptoms include abdominal pain (usually in the lower left side), fever, nausea, vomiting, changes in bowel habits, and sometimes rectal bleeding. Diverticulitis can vary from mild to severe, with potential complications like abscesses, perforation of the colon, or fistulas.