Tattooing involves the placement of pigment into the dermis. After the initial pigment injection, the presence of foreign material (the pigment) activates the immune system’s phagocytes (White Blood Cells) to engulf the pigment particles. As healing proceeds, granulation tissue forms, later it is transformed into a connective tissue as a result of collagen growth. This process mends the upper dermis, where pigment molecules remain trapped between fibroblasts. Ultimately, the pigment molecules concentrate in a layer just below the dermis/epidermis boundary and remain trapped inside for many years.
The energy of the light pulse is absorbed in the pigments of the tattoo, shakes the connections between the pigment molecules and gradually breaks the big pigment molecules constructions into smaller ones. As soon as a piece is small enough to pass between the cells, it is treated by the immune system as a foreign body and is driven out of the blood stream and the body. After several treatments, the tattoo fades away.