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Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal (GI) tract. IBS causes the large intestine (colon) to be become sensitized and overreactive, resulting in dysfunction. The three main types of IBS are defined by the primary symptom. More rarely, IBS types can be unspecified or based on the condition that led to the development of IBS.
Treatments for IBS often differ based on the type of IBS as person has.
In IBS-D, the person’s stools are loose more than 25 percent of the time, and stools are hard less than 25 percent of the time. Men are more likely than women to have IBS-D. People with IBS-D are more likely to report gas and sudden urges to defecate.
In IBS-C, the person’s stools are hard more than 25 percent of the time, and stools are loose less than 25 percent of the time. Women are more likely than men to have IBS-C. People with IBS-C are more likely to report infrequent defecation, straining to pass stool, and bloating.
Also referred to as alternating IBS (IBS-A), IBS-M causes both diarrhea and constipation more than 25 percent of the time.
People whose IBS symptoms follow an unusual pattern may be said to have IBS unspecified or unclassified (IBS-U).
People who develop IBS symptoms after a severe gastrointestinal infection are sometimes described as having post-infectious IBS (PI-IBS).
Some people develop IBS after a bout of diverticulitis – a condition that occurs when a pouch forms in the lining of the digestive system and becomes infected. People with this type of IBS may be said to have post-diverticulitis irritable bowel syndrome (PDV–IBS).