Does clinical testing support the current guidance definition of prolonged contact for nickel allergy?

BACKGROUND: The European Chemical Agency (ECHA) definition of prolonged contact was introduced in 2014 and has not been evaluated clinically. OBJECTIVES: To assess whether nickel-sensitized individuals react on patch testing with high nickel-releasing metal discs for short and repetitive periods. MATERIALS AND METHODS: We patch tested 45 nickel-sensitized individuals double-blind with 2 different types of high nickel-releasing discs for 10, 30 and 60 minutes on 3 occasions over a period of 2 weeks, and for 1 longer period. Discs were tested for nickel release. RESULTS: /week limit of the EU REACH nickel restriction. However, only 1 individual tested had a largely dose-dependent allergic reaction. CONCLUSIONS: The majority of nickel-allergic subjects did not react to nickel discs after 2 hours or after repetitive exposures of up to 30 minutes on 3 occasions over a period of 2 weeks. The length of time needed to cause nickel allergic contact dermatitis in most nickel-allergic individuals is longer than the ECHA guidance definition. Longer test times are needed to define the time required to cause dermatitis in most nickel-allergic individuals. As a limitation, the test conditions did not adequately assess real-life factors such as friction, which is relevant for some uses of nickel.