Tattoo darkening and nonresponse after laser treatment - A possible role for titanium dioxide

Objective: To examine relationships between chemical composition, biopsy fi ndings, and clinical outcome in laser-treated tattoos. Design: Observational nonblinded retrospective study. Settings: University-based dermatology clinic and private practice. Participants: Twenty patients who underwent biopsy of laser-treated tattoos . Main Outcome Measures: Biopsy specimens were analyzed after laser treatment , and the depths of changed particles were recorded. Ultrastructure of the changed particles was examined by electron microscopy. Presence of inorgani c chemicals was determined by x-ray diffraction. Correlation between x-ray diffraction, microscopy, and clinical response was attempted. Results: Of the 20 tattoos, 7 lightened, 9 failed to change, and 4 darkened after laser treatment. There was a significant association between presenc e of titanium dioxide and poor response to laser therapy. Microscopic studi es showed variable changes in the ink particles, but there was a trend towa rd residual deep green pigment in the resistant tattoos. Also, round dark s tippling was observed superficially in the darkened specimens. Conclusions: Titanium is overrepresented in tattoos that respond poorly to laser treatment. Further studies are necessary to show whether this metal i s the primary cause of this poor response.