[Adverse reaction to the azo dye Pigment Red 170 in a tattoo]

A 30-year old white male presented with sharply demarcated pruritic lesions in a black and red tattoo on his wrist. The strongly infiltrated and slightly scaly eruptions started four months after tattoo application and were notably restricted to the red-colored areas. Symptoms got worse after UV exposure. Patch testing and photo patch testing with the used azo dye Pigment Red 170 (C.I. 12475) was negative. Histology revealed lichenoid dermatitis without signs of a granulomatous reaction. The verification of allergic sensitization in hypersensitivity reactions to tattoos by patch testing may be difficult due to the poor penetration into the skin of the applied azo pigments. Intradermal testing may be more sensitive but bears the risk of long lasting skin reactions.