The oldest discovered tattoos date back over 5,000 years ago, yet despite their ancient origins, the process behind their permanency has remained unclear. Research has shown that macrophage dynamics is the key to their longevity. Macrophages are specialized cells involved in the destruction of bacteria and other harmful organisms. Tattoo needles punch through the epidermis of the skin and deliver ink to the second layer of skin, the dermis. The ink pigment is a foreign body, so the immune system responds and attempts to clear it. That’s why newly tattooed skin swells. Unlike bacteria, viruses and other foreign materials, the immune system has no effect on the ink. Since the macrophages can’t break down the ink, it remains trapped in the dermis. That’s what makes removing a tattoo so tricky. Although lasers break down the pigment and kill the cells, new macrophages are recruited to the damaged tissue and recapture much of the released pigment. That’s why tattoo removal takes multiple visits to totally remove the ink. The cost of tattoo removal doesn’t come cheap. The average price is $500 per session, with an average of six sessions required for total removal. The sessions typically last anywhere from 2-60 minutes, depending on the size of the tattoo.