The cause of IBS is not entirely understood by doctors or scientists, but they have been able to identify some possible factors which may predispose an individual to the condition. These include genetics and prior adverse life experiences, such as intestinal infection or childhood trauma. In addition, it seems that an overly reactive bowel can trigger or amplify symptoms, often in response to eating, stress, emotional arousal, gastrointestinal infection, menstrual period, and gaseous distension. Moreover, scientists have found that symptoms are linked to disturbances in colonic motility and food, gas, or stool sensitivities. By looking at both the physical processes involved in IBS and the various triggers of certain symptoms, we can better understand the condition.

The physical processes that are seen in people with IBS include slow or spastic movements of the colon, abnormal serotonin levels in the colon, and mild celiac disease. Colon movements that are too slow can result in constipation because too much water is absorbed, and spasms can result in painful cramps due to overly hard squeezing. Serotonin, a neurotransmitter that is involved in mood, can affect motility and bowel movements when its levels are too low or too high. Lastly, mild celiac disease can damage the intestines, and since IBS is a disorder of the large intestine, this can contribute to or worsen many of the symptoms.

Diet triggers are many and varied, and differ for IBS with constipation and IBS with diarrhea. Foods that make IBS-C worse include breads and cereals with refined grains, packaged and processed foods, dairy products such as cheese, coffee and alcohol, carbonated drinks, and high-protein diets. Foods that make IBS-D worse include large meals, fried and fatty foods, products with fructose or sorbitol, caffeine and chocolate, and high-fiber diets. In both cases, drinking plenty of plain water and staying away from gassy foods may help to ease symptoms of gas and bloating. Continuing on the topic of diet and food, dietary allergies and food sensitivities may also be at play.

Post-infectious IBS is caused by a previous bacterial infection of the gastrointestinal tract, which brings about the discussion of bacteria and IBS. There are trillions of bacteria in the bowel which help break down food and also help regulate bowel function. Additional functions of gut bacteria include protecting against infection, producing nutritional substances, and helping the gut immune system to develop. Evidence suggests that when the number or type of these bacteria changes, IBS symptoms may be triggered. For example, use of antibiotics or probiotics, low levels of inflammation, and small intestinal bacterial overgrowth may all be associated with IBS in some way or another.

Symptoms of IBS tend to worsen during periods of stress and anxiety, as well as during menstruation. Sources of stress and anxiety include work, problems at home, worries about money, and a general feeling of being out of control. As far as menstrual triggers go, women find that taking birth control pills or antidepressants can help. Other common triggers of IBS include eating while working or driving, chewing gum, and not getting enough exercise. Luckily all these potential causes and triggers can be reduced or completely eliminated by cutting out distractions, practicing mindfulness, and leading a healthy lifestyle.