The exposome in inflammatory bowel disease

Inflammatory bowel disease (IBD) including Crohn's disease (CD) and ulcerative colitis (UC), is an immunologically mediated chronic disease. The key underlying pathology is a deregulated immune response to commensal flora in a genetically susceptible host. Advances in genomics, epigenomics and understanding of the microbiome have brought forth the role of these spheres in the pathogenesis of IBD. Yet these factors explain only a small fraction of disease risk and our ability to predict relapses and response to treatment remains dismal. The external environment plays an important role in modifying the risk of IBD and in precipitating relapses in patients with established disease. The term 'exposome' was proposed to reflect a life-course of environmental influences beginning in-utero and proceeding right through childhood to adulthood. While the exposome is still a concept which needs practical perspective to enable better patient care, this review examines the gaps in our understanding that the IBD exposome helps explain. We further highlight the definition and parameters of this metric which can be incorporated for its application in research and clinical practice.