Background: High-energy, short-pulse lasers, eg, Q-switched lasers, emitting visible and near-infrared light have recently been developed for removing tattoos, with little risk of scarring. The mechanisms of action, and possible adverse effects other than scarring and hypopigmentation, are not fully understood.
Observations: We describe five cases of pulsed-laser-induced, immediate, irreversible darkening of cosmetic, white, flesh (skin-color), and pink-red colored tattoos. Irreversible ink darkening can be an insidious complication, because immediate whitening of the skin temporarily obscures the subsequently impressive color change. Among these cases, irreversible ink darkening occurred with Q-switched ruby (694 nm), Q-switched neodymium (Nd):YAG (1064 nm/532 nm), and pulsed green dye (510 nm) lasers. Attempts to remove the darkened ink with further laser treatment failed in two cases, and surgical excision was necessary. In the other three cases, subsequent laser treatments successfully removed the darkened ink. The red cosmetic tattoo ink used in one of the cases was placed in agar in vitro and was converted to a black compound immediately on Q-switched ruby laser exposure. Ferric oxide, a brown-red ingredient commonly used in cosmetic tattoos, was similarly tested and blackened in vitro by Q-switched ruby laser exposures.
Conclusions: Although most tattoos are not darkened by laser treatment, short-pulsed lasers over a wide spectrum can cause immediate darkening of some tattoo inks. Patients should be warned of the potential for irreversible cosmetic tattoo darkening, and test-site exposures should be performed prior to treatment. In some cases, subsequent laser treatments may remove the blackened ink. The mechanism probably involves, at least for some tattoos, reduction of ferric oxide (Fe2O3, "rust") to ferrous oxide (FeO, jet black), but the chemical reaction that is involved remains unknown.