The walls of the intestines are lined with layers of muscle that contract and relax as they move food from your stomach through the intestinal tract to the rectum. Normally, these muscles contract and relax in a coordinated rhythm. But if you have IBS, the contractions are stronger and last longer than normal. Food is forced through your intestines more quickly, causing gas, bloating and diarrhea. In some cases, however, the opposite occurs. Food passage slows, and stools become hard and dry.
No one knows exactly what causes IBS. Some researchers think IBS is caused by changes in the nerves that control sensation or muscle contractions in the bowel. Others believe the central nervous system may affect the colon And because women are two to three times more likely than men to have IBS, researchers believe that hormonal changes also play a role. For many women, symptoms are worse during or around their menstrual periods.
For reasons that still aren’t clear, if you have IBS you probably react strongly to stimuli that don’t bother other people. Triggers for IBS can range from gas or pressure on your intestines to certain foods, medications or emotions. Chocolate, milk and alcohol might cause constipation or diarrhea, for instance. And the least bit of stress might send your colon into spasms.
In fact, if you’re like most people with IBS, you probably find that symptoms are worse or more frequent during stressful events, such as a change in your daily routine or family arguments. But while stress may aggravate symptoms, it doesn’t cause them.