Histologic comparison of argon and tunable dye lasers in the treatment of tattoos.

Cosmetic benefit from laser therapy of tattoos may simply be the result of thermal injury and host reparative response which remove pigment by a "slough and bury" mechanism. Tattoo pigment of 4 colors (black, white, red, and blue) was introduced into the skin of guinea pigs and studied histologically at 48 h, 7 days, 4 and 6 weeks, and 3 months. Tattoos of each color were treated with argon laser (488 and 514 nm) and tunable dye laser at 3 different wavelengths (505, 577, and 690 nm). Treated tattoos were biopsied immediately and at 48 h, 7 days, and 3 months. Selective laser absorption by the tattoo pigment was suggested by pigment-related differences in threshold doses for histologic damage. Clinical clearing of tattoo pigment correlated well with the extent of immediate epidermal and dermal necrosis and was as well associated histologically with the deposition of parallel bands of collagen fibers (i.e., scar) between the residual pigment and the overlying epidermis. "Lightening" of tattoos probably depends more on widespread necrosis, subsequent tissue sloughing, and resultant dermal fibrosis than on specific changes in tattoo pigment chemistry, morphology, physical properties, or handling by macrophages.