IBS occurs when the muscles in the intestines don't work properly, and there is heightened pain perception in the colon. It is typically characterized by gas, abdominal pain, and diarrhea or constipation, or both. Some studies have shown that an imbalance of "good" and "bad" bacteria in the intestines may play a role in the development of symptoms for some people with IBS. Probiotics help restore the balance of bacteria in the intestinal tract to one that favors beneficial bacteria over potentially harmful bacteria. Research about the role that probiotics may play in this area is in the early stages.