Infections :No specific organism has been isolated for Crohn's but now mycobacteria paratuberculosis has attracted attention. The PCR method has identified mycobacterial TB DNA in the intestinal tissue of Crohn's disease.

Diet : There are an array of antibodies against food antigens, such as milk proteins & bakers yeast in Crohn's disease patients. In another study it was found that titanium, presumably of dietary origin in the intestinal transmural inflammatory infiltration of CD patients and in the Peyers patches suggested that dietary products are capable of being incorporated in the internal milieu

Genetics : A week association has been found between Crohn's disease and HLA - A2, HLA-DR4, DR1-DQ5 and inverse correlation with HLA-A11 & HLA-DR3. Association of the Crohn's with genetic disease has also been used as an indirect evidence. The diseases are ankylosing spondylitis, tyrosine positive albinism and Turours syndrome. An increased incidence of chromosomal breaks has been found in Crohn's disease patients compared with normal suggesting that inherited chromosomal fragility may be a factor in CD

Immune System : The normal gut flora is capable of suppressing the inflammatory process in the gut, but in CD this domain - regulation method is lost and therefore there is an intense inflammatory process. The gut epithelial cells are dysregulated i.e. the normal intestinal epithelium contains MHC class II and HLA DR-DP, which are important in processing other antigens. This distribution is changed on GI tract more so in the gut (intestine) in CD patients. The cells which usually stimulate proliferation of T suppressor cells in fact stimulate proliferation of T-helper cells. It is these T-helper cells which stimulate the cascade of immense activation.

Psychosocial factors: They represent a combination of external & internal factors. However Crohn's is not considered as a major psychosomatic disease in etiology.