Nickel Allergy and Piercings: A Systematic Review and Meta-Analysis.

Nickel is the most frequent cause of allergic contact dermatitis in Europe and worldwide despite 20 years of regulation. The aim of this study is to systematically assess (i) the risk of nickel allergy associated with piercings and (ii) the proportion of earrings for piercings on the market that release excessive amounts of nickel. The databases PubMed, Embase, and Web of Science were searched. Regarding (i): nickel allergy was significantly associated with piercings in the general population (OR 5.9 [95% CI: 3.6-9.4], n = 5333) and in dermatitis patients (OR: 3.6 [95% CI: 2.3-5.8], n = 20 330). The etiological fraction was 82% (95% CI: 55.2%-92.8%) and 69.7% (95% CI: 62.7%-75.3%), respectively. Regarding (ii): critical nickel release, as determined by dimethylglyoxime (DMG) screening, was identified in 11.3% of European earrings, while a much higher proportion was found in earrings from Asia (34.5%) and North America (31.1%). Of concern, as determined by EN1811, 24.7% of European earrings intended for piercing exceeded regulatory limits. In conclusion, piercing poses a significant risk factor for nickel allergy and a large proportion of earrings still release nickel in amounts that may result in nickel allergy and allergic nickel dermatitis. Stricter enforcement of existing regulations and consideration of new measures are essential.