Red tattoos, ultraviolet radiation and skin cancer in mice

Ultraviolet radiation (UVR) induces skin cancer. The combination of UVR and red tattoos may be associated with increased risk of skin cancer due to potential carcinogens in tattoo inks. This combination has not been studied previously. Immunocompetent C3.Cg/TifBomTac hairless mice (n=99) were tattooed on their back with a popular red tattoo ink. This often used ink is banned for use on humans because of high content of the potential carcinogen 2‐anisidine. Half of the mice were irradiated with three standard erythema doses UVR thrice weekly. Time to induction of first, second and third squamous cell carcinoma (SCC) was measured. All UV‐irradiated mice developed SCCs. The time to the onset of the first and second tumor was identical in the red‐tattooed group compared with the control group (182 vs 186 days and 196 vs 203 days, P=ns). Statistically, the third tumor appeared slightly faster in the red‐tattooed group than in the controls (214 vs 224 days, P=.043). For the second and third tumor, the growth rate was faster in the red‐tattooed group compared with the control (31 vs 49 days, P=.009 and 30 vs 38 days, P=.036). In conclusion, no spontaneous cancers were observed in skin tattooed with a red ink containing 2‐anisidine. However, red tattoos exposed to UVR showed faster tumor onset regarding the third tumor, and faster growth rate of the second and third tumor indicating red ink acts as a cocarcinogen with UVR. The cocarcinogenic effect was weak and may not be clinically relevant.