Photocytotoxicity in human dermal fibroblasts elicited by permanent makeup inks containing titanium dioxide

Titanium dioxide (TiO2) is a pigment widely used in decorative tattoo and permanent makeup inks. However, little is known about the risks associated with its presence in these products. We have developed an in vitro assay to identify inks containing TiO2 that are cytotoxic and/or photocytotoxic. The presence of TiO2 in ten permanent makeup inks was established by X-ray fluorescence. Using X-ray diffraction, we found that seven inks contained predominately TiO2 (anatase), the more photocatalytically active crystalline form of TiO2. The remaining inks contained predominately TiO2 (rutile). To identify cytotoxic and/or photocytotoxic inks, human dermal fibroblasts were incubated for 18 h in media containing inks or pigments isolated from inks. Fibroblasts were then irradiated with 10 J/cm2 UVA radiation combined with 45 J/cm2 visible light for determining photocytotoxicity, or kept in the dark for determining cytotoxicity. Toxicity was assessed as inhibition of colony formation. No inks were cytotoxic. However eight inks, and the pigments isolated from these inks, were photocytotoxic. Using ESR, we found that most pigments from photocytotoxic inks generated hydroxyl radicals when photoexcited with UV radiation. Therefore, the possibility of photocytotoxicity should be considered when evaluating the safety of permanent makeup inks containing TiO2.