Causes of IBS

The cause for IBS is unknown. Many health care providers agree that the discomfort often starts when muscles in the outer layer of the intestines do not relax and contract in sync with each other. Digestion occurs too quickly—leading to watery stool that must be eliminated urgently (diarrhea), or too slowly—resulting in dry, hard stool that is difficult to pass (constipation).

Researchers are investigating several possible causes for IBS. For example:

  • Hormonal changes may be a factor for women, since symptoms can worsen during menstrual periods.
  • The neurotransmitter serotonin, which transmits messages between parts of the body and is involved in sleep-waking cycles, is also present in the lining of the gastrointestinal tract. High levels of serotonin might cause a patient to be more sensitive to abdominal pain if signals between the brain and the intestines misfire.
  • The central nervous system can affect intestinal contractions.
  • The immune system and bacterial infections may be involved, since some patients who have gastroenteritis (infectious diarrhea) eventually develop IBS.
  • Celiac disease (also called celiac sprue) may contribute to IBS. Celiac sprue is an intestinal tract disease caused by difficulty digesting proteins found in wheat (e.g., gluten). Celiac disease causes an inadequate absorption of nutrients and weight loss, and may cause IBS symptoms.

Risk Factors for IBS

Irritable bowel syndrome is twice as common in women. Genetics (heredity) may play a role in IBS, but this is not yet known.

In some cases, IBS symptoms are triggered by the following:

  • Eating habits—Certain foods and beverages (e.g., chocolate, milk, alcohol, soda), large meals, and some medications can aggravate IBS symptoms. Fats and caffeine sometimes can cause intestinal cramping.
  • Smoking—Nicotine in cigarettes can worsen symptoms in some patients.
  • Stress—Symptoms may be more severe during times of stress.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 28 Feb 2008

Last Modified: 22 Sep 2015