Irritable bowel syndrome (IBS) usually begins in the late teens, 20s, or 30s. You're a relatively healthy person; then one day you begin to suffer intermittent cramps in the lower abdomen. You have to move your bowels more often than usual, and when you have to go, you have to get to a toilet right away. Your stools are loose and watery, possibly containing mucus. Sometimes, you feel bloated and full of gas.
After a while, the cramps return, but this time when you try to go to the bathroom, nothing happens. You're constipated. And back and forth it goes -- diarrhea, then constipation, and pain and bloating in between. Some people with IBS alternate between constipation and diarrhea, while others always have one without the other. Irritable bowel syndrome is the catchall term for this mixed bag of symptoms.
It's a common disorder, with no known cause. The most frequently reported symptom is pain or discomfort in the abdomen. People with IBS generally feel their pain subside after a bowel movement or passing gas. But they also may feel that they haven't fully emptied their rectum after a movement.
While some patients have daily episodes or continuous symptoms, others experience long symptom-free periods. These patterns make it hard to know whether someone has IBS or some occasional complaint that's part of the bowel's normal response to stress or diet. Whether it is IBS usually depends on the frequency and duration of symptoms: traditional criteria for this diagnosis are abdominal pain and changed bowel habits at least three times a month, for at least three months.
IBS has no organic basis -- that is, there's no physical abnormality or disease at the root of the problem. And doctors don't regard IBS as a forerunner of more serious diseases, such as ulcerative colitis, Crohn's disease, colon cancer, or stomach cancer.