Quantitative analysis of restricted metals and metalloids in tattoo inks: A systematic review and meta-analysis

The various ingredients and impurities that can be detected within tattoo inks have been associated with a myriad of dermatologic complications. Legislation regarding these antigenic substances varies widely around the world, with Europe serving as both the research and regulatory center on these intradermal formulations. Although industry is said to be moving away from metallic and metalloid pigments in exchange for organic or organometallic dyes, surveys of commercially available inks continue to detect these elements at concentrations considered unsafe for application into the dermis. In order to better assess the formulation and safety of tattoo ink, we present a systematic review and meta-analysis of studies quantifying restricted metals and metalloids in commercially available tattoo ink products. Among the papers selected, inconsistencies were noted in the degree of specificity by which ink products were identified and the elements sampled for. In addition, the analytical targets' valency and/or solubility were not always considered in accordance with regulation criteria. Of note, chromium, by total content and that of its regulated +6 valency, exceeded its maximum allowed concentration in nearly every sample tested. Total copper content exceeded the limit for soluble copper in half of inks sampled. In descending order, concentrations of cadmium, barium, mercury, soluble copper, arsenic, zinc, antimony, and lead violated regulations in one-sixth or fewer of samples tested. Cobalt and tin levels never violated regulation. Overall, our findings indicate that unsafe levels of restricted elements continue to be detected across studies, warranting further investigation under a regulatory lens.