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: Nickel release from both discs significantly exceeded the 0.5 μg Ni/cm(2)/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.