How Tattooing Really Works
1. Tattooing causes a wound that alerts the body to begin the inflammatory process, calling immune system cells to the wound site to begin repairing the skin. Specialized cells called macrophages eat the invading material (ink) in an attempt to clean up the inflammatory mess.
2. As these cells travel through the lymphatic system, some of them are carried back with a belly full of dye into the lymph nodes while others remain in the dermis. With no way to dispose of the pigment, the dyes inside them remain visible through the skin.
3. Some of the ink particles are also suspended in the gel-like matrix of the dermis, while others are engulfed by dermal cells called fibroblasts. Initially, ink is deposited into the epidermis as well, but as the skin heals, the damaged epidermal cells are shed and replaced by new, dye-free cells with the topmost layer peeling off like a healing sunburn.
4. Dermal cells, however, remain in place until they die. When they do, they are taken up, ink and all, by younger cells nearby so the ink stays where it is.
5. So a single tattoo may not truly last forever, but tattoos have been around longer than any existing culture. And their continuing popularity means that the art of tattooing is here to stay.
From the TED-Ed Lesson What makes tattoos permanent? - Claudia Aguirre
Animation by TOGETHER