IBS-Irritable Bowel Syndrome a personal view of Causative Factors
The primary cause of IBS (irritable bowel syndrome) is excessive spasms of the large intestine.
Some other causative factors in IBS (irritable bowel syndrome) are a low fibre diet, food sensitivities, intestinal candidiasis and psychological stress.
Contributing psychological factors include stress, excitement, nervousness, anxiety, guilt and depression. Mental or emotional problems such as anxiety, fatigue, hostile feelings, depression and sleep disturbances are reported by almost all patients with IBS (irritable bowel syndrome).
There are theories that link psychological factors to the symptoms of IBS and personality assessments of IBS (irritable bowel syndrome) sufferers have shown them to have higher anxiety levels and a greater feeling of depression. However, these studies were based on personality assessments after the individual developed IBS (irritable bowel syndrome). It has since been determined by pre-illness personality assessment that IBS (irritable bowel syndrome) sufferers have normal personality profiles. Therefore, many of the psychological symptoms may be either secondary to the bowel disturbances (particularly malabsorpion) or the result of a common causative factor, e.g., stress, food allergy, environmental illness, or candidiasis.
Physical factors include: 
Heavy smoking
Poor diet
Food allergies (for instance wheat intolerance)
Coffee
Raw fruits and vegetables
Food poisoning
Drugs, especially improper use of laxatives
Diverticular disease
Colon cancer
Other illnesses
Intolerance of lactose:
Lactase is the enzyme in the small intestine that digests lactose (the naturally occurring sugar in milk). A few children and many adults do not produce sufficient lactase, resulting in impaired ability to digest milk. These people are lactose intolerant and often suffer from symptoms including cramps, wind, indigestion, heartburn and diarrhoea. Lactose intolerance could be confused with a dairy allergy therefore a diagnosis by your Doctor is the best course of action.