Photostability and breakdown products of pigments currently used in tattoo inks

Tattoos fade with time. Part of this fading can be attributed to the photodegradation of pigments. When people get tired of their tattoos, removal by laser irradiation is the method of choice. In vivo laser irradiation of tattoos on mice has shown that the degradation of pigments can result in toxic compounds. Various in vitro studies on photodegradation by sunlight or laser have shown similar degradation products for both irradiations. Even visible light was shown to be able to decompose some pigments to toxic degradation products in vitro. Whereas the investigated phthalocyanins (C.I. 74160, 74260), quinacridones (C.I. 73915) or dioxazines (C.I. 51319) were fairly photostable in vitro, all azo pigments exposed to sunlight or laser were degraded into a variety of products, some of which were toxic or even carcinogenic, such as 2-amino-4-nitrotoluene, 3,3'-dichlorobenzidine and o-toluidine. Up to now, the absence of specific toxicological data is the reason why legal restrictions for tattoo inks are derived from those for cosmetics, toys and textiles. Photodegradation has not been considered. In light of the present analytical findings, even with their possible shortcomings, the evidence weighs heavily enough to consider banning azo pigments containing carcinogenic aromatic amines or allergens in their structure from use in tattoo inks.