THE SCIENCE BEHIND TATTOOS
Tattoos are becoming more popular, acceptable and spoken about; but not everybody knows how a tattoo actually works.
The dictionary definition of a tattoo is to “Mark (a part of the body) with an indelible design by inserting pigment into punctures in the skin”. For the tattoo to be permanent, the ink must sit in the dermis, this is the tissue that sits just underneath the outer layer of the skin, called the epidermis. The dermis is a thick layer of fibrous and elastic tissue, made up of mostly collagen with a small amount of elastin; this gives the skin its strength and flexibility. It also contains nerve endings, sweat glands, oil glands, hair follicles and blood vessels.
The ink must enter the dermis and not the epidermis as the outer skin cells of the epidermis are continually dying, breaking away and falling off. If a tattoo was to enter this layer it would begin to ‘disappear’ in a matter of weeks.
For the ink to enter the dermis, the needle, affixed to the tattoo machine, makes thousands of tiny punctures in the skin. The needle punctures the skin repeatedly and quickly, as it does this the ink is dragged downwards into the dermis.
A tattoo is an open wound; therefore, the body is alerted to begin the inflammatory process and the body’s immune system kicks in, sending macrophage cells to the location of the tattoo to consume the ink particles; which it sees as a foreign body. Macrophage cells are specialist cells that protect the body by ingesting harmful, foreign particles, bacteria and dead or dying cells.
Once the macrophage has consumed an ink particle, it goes back through the lymphatic system and takes the ink particles to the liver for excretion. The macrophage cells do not eat all the ink that has entered the dermis. The ink that remains in the dermis is within trapped microphages or skin cells called Fibroblasts. Fibroblasts are types of cell that are responsible for generating connective tissue; they also play a critical role in immune response.
Researchers have always wondered how microphages stay put for so long and how a tattoo remains once those cells have died! A recent study published in the Journal of Experimental Medicine suggests that when the microphage cells die, they leave the ink among skin cells; like at the very start of the tattoo process. New microphages travel to the area to consume the remaining ink, and the process starts all over again.
Sources: British Society for Immunology
Journal of Experimental Medicine
Molecular Biology of the Cell. 4th edition
Tattoo Lasers & Histology by Suzanne Kilmer