Objective: Inflammatory bowel disease (IBD) has previously been investigated with relation to allergic conditions; however, diverging results were found and there are only a few small studies focusing on delayed hypersensitivity. The aim of this study was to investigate whether there was an association between contact allergy (CA), which is a type IV hypersensitivity reaction of the skin, and IBD.
Material and methods: A database consisting of a cohort of 13,315 patients, patch tested between 1985 and 2003, was linked with the Danish National Patient Registry using a unique personal identifier number. The patients were patch tested at a dermatology department with a long history of research in CA. By record linking with the Danish National Patient Registry, patients were identified who had either an International Classification of Disease (ICD) code for Crohn's disease (CD) or an ICD code for ulcerative colitis (UC) diagnosis. Using logistic regression, with the result of the patch test as the dependent variable, we calculated the odds ratios for IBD, CD and UC, adjusted for gender and age.
Results: An inverse association between CA and IBD was found, odds ratio adjusted for age and gender 0.71 (CI 95% 0.53-0.94), which is mainly the result of an inverse association between CA and CD, odds ratio adjusted for age and gender 0.42 (CI 95% 0.23-0.76).
Conclusions: The association found between CA and IBD might be related to shared genetic factors or common environmental determinates. It may also be that having either disease result in skewness of the immune system might lead to an inverse disease association.