These disorganized, exaggerated and painful contractions lead to certain problems. The pattern of bowel movements is often altered. Diarrhea may occur, especially after meals, as the entire colon contracts and moves liquid stool quickly into the rectum. Or, localized areas of the colon may remain contracted for a prolonged time. When this occurs, which often happens in the section of colon just above the rectum, the stool may be retained for a prolonged period and be squeezed into small pellets.
Excessive water is removed from the stool and it becomes hard.
Also, air may accumulate behind these localized contractions, causing the bowel to swell. So bloating and abdominal distress may occur. Some patients see gobs of mucous in the stool and become concerned. Mucous is a normal secretion of the bowel, although most of the time it cannot be seen. IBS patients sometimes produce large amounts of mucous, but this is not a serious problem.