The "hygiene hypothesis" for Crohn's disease postulates that multiple childhood exposures to enteric pathogens protect an individual from developing Crohn's disease later in life, while individuals raised in a more sanitary environment are more likely to develop Crohn's disease. In this issue of the American Journal of Gastroenterology, two Canadian case-control studies come to diametrically opposed conclusions regarding the hygiene hypothesis for Crohn's disease. This difference may be partially related to differences in study population (population based vs hospital based), age of onset, different genetic determinants, urban/rural residence (40% rural vs principally urban), or different exposures from the putative causative agent. As of now, the veracity of the hygiene hypothesis for Crohn's disease is not confirmed.
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