Fluctuations in the prevalence of nickel and cobalt allergy in eczema patients patch tested after implementation of the nickel regulation in Denmark

Objectives. To examine fluctuations in the prevalence of nickel and cobalt allergy after implementation of the nickel regulation, by analysing patch test results from male and female patients with dermatitis tested between 1992 and 2009 at Odense University Hospital, Denmark. Methods. A retrospective analysis of patch test data was performed (female, n = 5821; male, n = 3317). Comparisons were made using the chi-square test for trend. Logistic regression analyses were used to test for associations. Results. The prevalence of nickel allergy decreased significantly among the 2-30-year-old female patients, from 29.8% in 1992-1997 to 19.6% in 2004-2009 (p < 0.001), whereas it increased significantly, from 6.9% in 1992-1997 to 11.1% in 2004-2009 (p = 0.04), among the > 60-year-old female patients. The overall prevalence of cobalt allergy increased significantly, from 3.7% in 1992-1997 to 5.1% in 2004-2009 (p = 0.03). The overall prevalence of nickel and cobalt allergy among male patients during the test period was 5.2% and 2.2%, respectively, and no significant change across the test years was detected. Conclusions. The prevalence of nickel allergy decreased among young female patients and increased among older female patients with dermatitis, probably because of a cohort effect. The overall prevalence of cobalt allergy increased from 1992 to 2009. No significant trend in the prevalence of nickel and cobalt allergy among male patients was found.