The Possible Causes of Irritable Bowel Syndrome

Although doctors are not entirely sure what causes IBS, many suspect that abnormalities in the contractions of the intestinal wall are ultimately to blame. Normally, the muscles in the intestinal wall contract regularly and rhythmically, moving food smoothly from the stomach to the anus. In individuals with IBS, this process doesn’t seem to work quite right.

Individuals who experience abnormally rapid and strong contractions of the intestinal wall find that food moves too quickly through the digestive tract. Normally, undigested food residue has excess water removed in the rectum, in order to form normal stool. However, if the digestive tract is moving the food through the intestines too quickly, the water cannot be removed and the food cannot be properly digested. The result is unpleasant bloating, gas, and diarrhea. Conversely, individuals who experience slow and weak contractions of the intestinal wall may find themselves troubled by constipation due to the food travelling through the tract at an abnormally slow rate. Many IBS sufferers alternate between the two states.

Possible causes of IBS include:

  • Abnormalities of the gastrointestinal nervous system
  • Poor communication between the gastrointestinal system and the brain
  • Food allergies or intolerances
  • Stress
  • Hormonal changes
  • Bacterial overgrowth in the intestine

Nervous System Abnormalities

Some doctors believe that individuals affected by IBS may have abnormalities of the nervous system that controls the digestive tract. These abnormalities may lead to individuals experiencing discomfort from normal digestive tract activity, sensations that most individuals do not consciously experience or do not experience as uncomfortable. However, while this theory may explain the uncomfortable bloating sensations IBS sufferers experience, it does not fully explain the diarrhea and constipation.

Poor communication between the gastrointestinal system and the brain may, in part, be behind the alterations in intestinal contractions that occur in IBS. Poor communication may explain the digestive tract’s inability to maintain a normal regimen of intestinal contractions in response to external stimuli and food consumption.


Many IBS sufferers are fully aware that their symptoms flare up in response to certain external stimuli. Through experimentation, some have found that certain foods seem to trigger flares. These food responses do not seem to be classic allergic responses; rather, they seem to be food intolerances. IBS and foods that cause flares seem to be entirely individual, with no common pattern.

What causes IBS to flare up in most people is stress. Stress is well-known to affect the digestive tract. It is common for stress to trigger nausea, diarrhea, vomiting, anorexia, or over-eating even in people who do not have IBS. Abnormal communication between the brain and the digestive tract in individuals affected by IBS may explain the extreme digestive tract response to stress these people experience.

Women often experience flares in response to hormonal changes throughout the menstrual cycle. Other sufferers find that episodes of gastroenteritis, food poisoning, or alterations in the bacteria that colonize the gut, such as after taking antibiotics, cause severe flares in IBS symptoms.

IBS testing is generally a process of eliminating other causes of the troubling symptoms. There is no specific diagnostic test for IBS. Most diagnoses are made on the basis of the clinical presentation after performing tests to rule out other possible causes.