Nickel is the most frequent cause of contact allergy worldwide and has been studied extensively. This clinical review provides an updated overview of the epidemiology, exposure sources, methods for exposure quantification, skin deposition and penetration, immunology, diagnosis, thresholds for sensitization and elicitation, clinical pictures, prevention, and treatment. The implementation of a nickel regulation in Europe led to a decrease in the prevalence of nickel allergy, and changes in the clinical picture and disease severity. Nevertheless, the prevalences of nickel allergy in the European general population are approximately 8% to 19% in adults and 8% to 10% in children and adolescents, with a strong female predominance. Well‐known consumer items such as jewellery and metal in clothing are still the main causes of nickel allergy and dermatitis, although a wide range of items for both private and occupational use may cause dermatitis. Allergic nickel dermatitis may be localized to the nickel exposure site, be more widespread, or present as hand eczema. Today, efficient methods for exposure quantification exist, and new insights regarding associated risk factors and immunological mechanisms underlying the disease have been obtained. Nevertheless, questions remain in relation to the pathogenesis, the persistent high prevalence, and the treatment of severe cases.

BackgroundExposure to nickel releasing ear piercing jewellery may explain the persistently high prevalence of nickel allergy in Europe. While nickel release from earrings is regulated, field studies show that the regulation is not always respected. More knowledge is needed regarding the risk of piercing exposure including suitable screening methods.ObjectiveTo examine the proportion of earrings on the Danish market that release more nickel than allowed, and to validate the use of the dimethylglyoxime (DMG) test as a screening tool.MethodsA total of 304 earrings were purchased and tested with the DMG test and X‐ray fluorescence spectrometry. The level of nickel release was quantified in a selected subsample of 100 earrings by the European reference test EN 1811. The DMG spot test was validated against EN 1811 at different thresholds.ResultsExcessive nickel release according to the European regulation was found in 45 (14.8%) tested earrings. The sensitivity of the DMG test decreased with reduced levels of nickel release (sensitivity of 45.2% at ≥0.2 μg/cm2/week vs 61.1% at >0.5 μg/cm2/week).ConclusionExcessive nickel release is common in earrings on the Danish market. Because of low sensitivity, the DMG test has limited use in screening of earrings for research but may still be used clinically.

Background Chromium and cobalt are important skin sensitizers. It has, however, been difficult to identify causative exposures. Studies on nickel allergy have demonstrated piercing as critical for both sensitization and elicitation. It may be speculated that the same applies for chromium and cobalt. Objective To examine the content and release of chromium and cobalt from earrings randomly purchased in Denmark. Methods Three hundred four earrings were examined with x‐ray fluorescence (XRF) spectrometry. Earrings with measured content of chromium or cobalt were spot tested with diphenylcarbazide spot test (n = 166) or Nitroso‐R spot‐test (n = 99), respectively. Chromium and cobalt release were quantified in a selected subsample (n = 100) with the artificial sweat test (EN 1811). Results Chromium was present in 54.6% (166/304) of earrings and cobalt was present in 72.0% (219/304),− measured by XRF. All chromium spot tests for chromium VI were negative. The cobalt spot test was positive for one component. Chromium release was found from 59/100 (median concentration = −0.06 μg/cm2/week) and cobalt release from 29/100 (median concentration = −0.06 μg/cm2/week) of earrings in tested subsample. Conclusion Earrings for piercing release chromium and cobalt and may on a case basis be a source of chromium and cobalt allergy.

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