tattoo is a marking made by inserting indelible ink into the dermis layer of the skin to change the pigment

Tattoo histology

Tattooing involves the placement of pigment into the skin’s dermis, the layer of dermal tissue underlying the epidermis. After initial injection, pigment is dispersed throughout a homogenized damaged layer down through the epidermis and upper dermis, in both of which the presence of foreign material activates the immune system’s phagocytes to engulf the pigment particles. As healing proceeds, the damaged epidermis flakes away (eliminating surface pigment) while deeper in the skin granulation tissue forms, which is later converted to connective tissue by collagen growth. This mends the upper dermis, where pigment remains trapped within fibroblasts, ultimately concentrating in a layer just below the dermis/epidermis boundary. Its presence there is stable, but in the long term (decades) the pigment tends to migrate deeper into the dermis, accounting for the degraded detail of old tattoos.
Most modern tattoos are produced with an electrically powered machine that rapidly moves a needle up and down so that the insoluble micrometer-sized particles of ink it contains are injected into the skin quickly and at an even depth, generally one-eighth inch past the skin’s surface.  Here we see the black ink particles in an irregular connective tissue

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