Prevalence of nickel and cobalt allergy among female patients with dermatitis before and after Danish government regulation: a 23-year retrospective study.

BACKGROUND: An increased prevalence of nickel allergy prompted the Danish government to prohibit excessive nickel release (ie, >0.5 microg nickel/cm(2)/wk) from consumer products in 1990. Concomitant allergy to nickel and cobalt is often observed among patients with dermatitis, probably as a result of cosensitization.
OBJECTIVES: The study investigated the development of nickel and cobalt allergy among Danish female patients with dermatitis tested between 1985 and 2007. This was done to examine whether Danish nickel regulation has reduced the prevalence of nickel allergy and to examine whether the prevalence of cobalt allergy has increased as a result of the nickel regulation.
METHODS: A retrospective analysis of all patch test data from our database was performed (n = 10,335). Comparisons were made using a chi-square test for trend. Logistic regression analyses were used to test for associations.
RESULTS: The prevalence of nickel allergy decreased significantly among those aged 5 to 30 years from 27.6% in 1985 to 16.8% in 2007 (P(trend) < .002) but increased among those aged 31 to 49 years from 21.3% to 33.8% in the same period (P(trend) < .001). The median age was significantly higher among patients with isolated cobalt allergy than among patients with nickel allergy (P < .001). LIMITATIONS: No information on causative exposures was available.
CONCLUSIONS: Nickel allergy decreased among young female patients with dermatitis between 1985 and 2007 whereas it increased among older patients, probably as a result of a cohort effect. The prevalence of cobalt allergy remained relatively unchanged.