As the symptoms of IBS may resemble other conditions such as colitis, diverticular disease, stomach ulcers and even cancer, it is important to consult a doctor to confirm the diagnosis.

Epidemiology

Most of the available data on IBS comes from the West: - Between 10% and 20% of the population are affected, with the female to male ratio at 1.5 to 2.0.

In a population-based cross-sectional survey conducted in 1999 by a team from the National University of Singapore, where 2,276 people were interviewed in their homes, IBS was found to affect about 1 in 10 people.

Women between 20 and 40 years of age had the highest frequency (16%) and men aged 50 years and above had the lowest (5%). Interestingly, well-educated women (those with a secondary and tertiary education, comprising 14% of those surveyed) were at high risk for IBS, and less well-educated men (those with a primary education, constituting less than 5% of the population surveyed) were at low risk.

Among patients consulting general practitioners for abdominal symptoms, 30% had IBS; for those consulting specialists (gastroenterologists), the incidence was 21%. IBS, together with functional dyspepsia, a related condition, accounted for almost half the consults. The ratio of female to male patients was 1.5:1.

Natural history

Most people with IBS experience intermittent symptoms: they will have good times and bad times. A small number have symptoms only once in a long while, others suffer every day. It has been estimated that in 1 year, 5% to 30% of people with IBS will lose their symptoms. However, during this time an equal number of people who did not have the condition will develop it, so that the number of people with IBS is kept relatively constant.

It is thus projected that most people will experience IBS at some time in their lives. For some, symptoms may change with time. In about 22% cases, bowel disturbances become less prominent and the pain and discomfort centres in the upper abdomen. When IBS patients were followed up for more than 5 years, less than 5% developed a more serious abdominal condition.

流行病学

IBS 的资料多来自西方，约有10%至20%的人口患上此病。其中女性与男性的比例为1.5到2.0比1。一九九九年，一组新加坡国立大学进行的抽样人口考察对 2,276人进行家访，发现10人中有一人患上IBS，20到40岁的女性占大多数（16%）五十岁以上的男性为数最少（5%）。有趣的是，受高深教育的 女性（中学和大学教育，占受查勘者的14%）患率甚高。反之，受低教育的男性（小学教育，占接受查勘者的5%）患上 IBS 的病率也低。

有肠胃病症状而去求医於普通医生者，30%患有IBS，求医於肠胃专科医生的病人中，有21%是IBS患者，而其中有将近一半的患者有IBS兼机能消化不良，女性病患与男性病患的比例为1.5:1。

IBS的进展许多IBS患者都有断续的症 状: 他们时好时坏。一小部份的症状很久才一次，一些每天都得忍受。估计在一年内有5%至30%的IBS患者的症状会消失。然而，就在同一时期会有相等数量的人 开始发现症状，这导致IBS患者的数目一直维持在一定的水平。这显示大部份人的一生中都会在某一段时期经历IBS症状。某一些人的症状会有所变动。在大约 22%的例子里，他们的肠胃不适变得不太明显而这些不适反而集中到腹部上端。在那些IBS超过5年以上复诊的患者里，少过5%的腹部不适会恶化。