Objective: To examine relationships between chemical composition, biopsy findings, 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 inorganic 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 presence of titanium dioxide and poor response to laser therapy. Microscopic studies showed variable changes in the ink particles, but there was a trend toward residual deep green pigment in the resistant tattoos. Also, round dark stippling 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 is the primary cause of this poor response.