Inverse relationship between allergic contact dermatitis and type 1 diabetes mellitus:: a retrospective clinic-based study

Aims/hypothesis: Contact allergy (CA) is a disease induced and maintained by environmental factors, which mainly has a Th2 pattern in its chronic form. Environmental factors play a major role in CA, while genetic factors are of minor importance. Type 1 diabetes is an autoimmune disease of the islets of Langerhans, which has a Th1 cytokine pattern and in which modulators of risk are both genetic and environmental. To investigate whether environmental exposure to chemicals leading to CA could influence the risk of type 1 diabetes, we conducted a retrospective clinic-based study of patients subjected to diagnostic patch testing of CA. Methods: We undertook a retrospective clinic-based study of 13,315 patients who were patch-tested between 1985 and 2003, and linked it with the Danish National Patient Registry containing diabetic mellitus discharge diagnoses from 1987 to 2003. The 13,315 patch-tested patients gave rise to 4,848 CA patients. Using logistic regression, we calculated odds ratios for persons with CA of having type 1 diabetes. Results: Type 1 diabetes was diagnosed in 229 of the patch-tested patients. CA patients had a reduced risk of having type 1 diabetes, with an odds ratio 0.62 (95% CI 0.46-0.86). After adjusting for sex and age, the odds ratio was 0.63 (95% CI 0.47-0.86). Conclusions/interpretation: An inverse relationship between CA and type 1 diabetes was found. Thus there may be a protective effect of having CA in relation to the risk of type 1 diabetes, or vice versa type 1 diabetes may lead to tolerance rather than hypersensitivity. Alternatively, these two diseases may share common genetic factors, although at present these are unknown.