Tattoo-induced immunologic reaction to red inks.

A 43-year-old male presented with pruritic nodular lesions in the red dye area of his leg tattoo, which developed 4 weeks after its application. Patch tests were performed using a standard series, and the inks used by the tattooist were tested semi-open. Tests identified a sensitization to 2 inks containing an azo-organic dye (Pigment Red 170), diketopyrrolopyrrole (Pigment Red 254), and copper phthalocyanine (Pigment Blue 15). Histopathological findings suggested a pseudolymphoid reaction, likely driven by T-cell hypersensitivity to the red pigments. Although the utility of patch testing in the assessment of tattoo reactions is not consensual, it can be useful in identifying the offending inks, helping to guide future tattoo choices and prevent recurrences. Patch testing including the suspected ink should not be disregarded from the diagnostic workup.