Irritable bowel syndrome, or IBS, is a group of symptoms that affect your digestive system. It’s a common but uncomfortable gastrointestinal disorder. People with IBS get excessive gas, abdominal pain, and cramps. The most common symptoms of irritable bowel syndrome (IBS) are a pain in your abdomen, often related to your bowel movements, and changes in your bowel movements. These changes may be diarrhea, constipation, or both, depending on what type of IBS you have. The exact cause of IBS is unknown. Possible causes include an overly sensitive colon or immune system dysfunction.