Despite extensive and continuing research, the cause is still unknown. However, there appears to be interplay between the genes and environmental factors, which in turn triggers the immune system to cause chronic damage in a susceptible individual. Quite how and when this happens may vary considerably and some of these issues are considered below:

1. Genetics and heredity
There is a slightly increased risk of developing ulcerative colitis if a near relative has the disease. Twin studies have shown that there is a higher incidence of ulcerative colitis amongst identical twins than in non-identical twins, suggesting a genetic link. However, this association is more pronounced in Crohns disease

2. Infection
Some cases of ulcerative colitis start after an episode of gastroenteritis.

3. Psychological factors
Persons affected are often 'high achievers’. Although stress is not a proven cause of the disease, it can make it worse.

4. Immunological factors
It is possible that the body's own defence system (immune system) is acting against the bowel lining and many drugs used to treat ulcerative colitis affect the immune system. However, it is likely that immunological changes are produced after the disease started, rather than causing it.

5. Non-steroidal Anti-inflammatory drugs (NSAIDS)
Although not a direct cause of colitis, NSAIDS are well known to provoke an attack once the disease has developed. This may be due to a breach in the protective barrier of the intestinal lining allowing the luminal contents to come into contact with it thus triggering an immune response within the tissue and consequent damage.

6. Smoking
Many cases of colitis begin on or shortly after giving up smoking. The reasons for this are not clearly understood but smoking appears to protect against the development of colitis. However, for other more important health reasons, it is not recommended that you continue to smoke or indeed start doing so having never smoked.

7. Diet
Dietary residues (mainly short-chain fatty acids) resulting from the fermentation of carbohydrates by the colonic bacteria are essential for the maintenance of healthy colonic cell function. There is evidence to suggest that the process by which these residues are taken up into the cells is impaired in ulcerative colitis, possibly due to the presence of a toxic substance called hydrogen sulphide, produced by certain bacteria acting on sulphur additives within the diet.