No one will give you a specific cause of IBS. IBS is a motility disorder some experts say.  An oversensitive or hyperactive gut is another possible cause of IBS. and the gut will react to changes influenced by stress, food and hormones.

Typically the bowel habit in IBS becomes chaotic. There is no surprised, therefore that it is considered a motility disorder. The transit time from ingestion of food to excretion is abnormal.

In diarrhoea the transit time is faster and in constipation it is slower. There are two types of IBS, diarrhoea predominant and constipation predominant. In some cases constipation and diarrhoea alternate. Stools in IBS can vary from hard pellets to watery and unformed.

Some say there is a link between diet and IBS.
Certain foods will trigger IBS symptoms. Intestinal gut activity is stimulated by ingesting food. This is a normal action and the most common is the Gastro colic reflex. This reflex is strongest after breakfast. Gastro-Colic reflex in IBS is strongest after fatty or large meals. This strong gut contraction can cause abdominal pains and or diarrhoea.

There is no evidence that food causes IBS but certain foods and the volume consumed at one time can trigger symptoms.

One suggestion is that it is a brain-gut disorder. The Enteric Nervous System is a complex interconnection of brain cells in the gut. To understand IBS, experts think you need to understand how the Enteric Nervous System works.

The Gut has the richest supply of serotonin in the body. This chemical is closely connected to the nervous system. At present a lot of research is focused on gut serotonin receptors.

Contractions of the smooth muscles of the gut are affected by serotonin. Low levels of serotonin lead to constipation and higher than normal levels cause diarrhoea.

Psychological factors such as anxiety, stress and depression can affect the gut. In addition psychological trauma such as physical, emotional and sexual abuse can affect the gut. Statistics show that there is a greater incidence of psychological trauma and disturbances in IBS. It is suggested that in addition to treating the IBS, treating the other issues will give better long-term results.

Gastroenteritis as a cause of IBS: Between 20-30% of patients who develop severe gastroenteritis will go on to develop IBS. The common infective organisms are Campylobacter jejuni, Salmonella shigella, and Escherichia coli. Serotonin levels in gastro-enteritis is very high and in cases that develop IBS this high level continues.

In some women, symptoms fluctuate during the menstrual cycle. The two hormones that control the menstrual cycle are oestrogen and progesterone. The passage of food residue along the large gut is affected by the female hormones.

Prof. Jonathan Brostoff of Middlesex Hospital believes that yeast is involved in some cases of IBS. An overgrowth of Candida occurs when there is reduced levels of good bacteria, Lactobacilli and Bifidobactreia.