IBS is a functional gastrointestinal disorder that primarily affects the gut and does not cause physical damage to the colon. On the other hand, ulcerative colitis is a structural disease that can affect the entire body and can cause physical damage to the colon. If left untreated, ulcerative colitis can lead to severe complications. The inflammation associated with ulcerative colitis can spread deep into the colon, potentially resulting in conditions such as toxic megacolon, which can lead to a ruptured colon, kidney failure, or a severe infection. Prompt treatment is crucial to prevent these serious complications.