Histopathology of Red Tattoo Reactions

Background: Despite popularity of tattoos, complications may occur. In particular, red tattoo reactions due to allergic reactions are the most frequent chronic tattoo reactions. However, little is known about its histopathology and underlying pathomechanisms. Objective: The aim of this article is to analyze the histopathology of red tattoo reactions for diagnostic purposes and to acquire more insight into pathogenesis. Methods: A retrospective cross-sectional study was conducted by reviewing the histopathology of 74 skin biopsies of patients with allergic red tattoo reactions. Histopathological findings, such as inflammation patterns, inflammatory cells and pigment depth and color, were semi-quantified with an in-house validated scoring system by 2 independent senior investigators. Results: Histiocytes and lymphocytes were both present in >93%. Histiocytes were the predominant inflammatory cells in 74.3%, but well-defined granulomas were mostly absent (78.0%). Eosinophils were uncommon (8.1%) The predominantly histiocytic reaction combined with interface dermatitis was the main inflammation pattern (37.9%). Most biopsies showed more than one reaction pattern. Interface involvement was observed in 64.8%, despite the intended depth of standard tattoo procedures, in which pigment is placed deeper, in the upper- and mid-dermis. Statistical analyses showed a significant association between inflammation severity and pigment depth (P = 0.024). In 6 cases (8.1%) pigments could not be retrieved histologically. Conclusions: In this cohort we demonstrated that cutaneous reactions to red tattoo ink are frequently characterized by the combination of dermal predominantly histiocytic infiltrates and epidermal interface dermatitis. Allergic reactions to red tattoo pigments probably represent a combination of a subtype IVa and IVc allergic reaction. Clinicians should be aware of the specific histopathology of these reactions and therefore the importance of taking a diagnostic skin biopsy.