Tattoo is a body modifications where an ink is applied to the skin where it can stay permanently. That is nice enough for a definition but how exactly all that works on macroscopic and microscopic level? We'll try to explain it here.
Let's say that you want a tattoo on your skin. You find a respectable tattoo parlor with a professional tattoo artist that knows his or her job and you like how they work. You already know what design you want on yourself or you choose from a “flash” of that tattoo parlor – a catalog of designs that parlor can offer you as an inspiration. Before tattoo artist starts tattooing he needs to sterilize all the items he will use (except those that are one-use-only like needles and gloves). Sterilization is done with autoclave which uses combination of steam, pressure, and heat to kill all microorganisms that can be found on instruments.
Artist also disinfects work area and show the client that tools have been disinfected. Place on the skin where the tattoo will go is then shaved and disinfected with antiseptic soap and water. Artist creates a stencil from the design and uses it to transfer a basic drawing of a design to a skin. He uses a needle and thin ink to draw an outline of the design which will help the artist to more precisely draw on the skin. Drawing is often done from bottom up so a stencil would not be smeared. When the outline is done, artist cleans the area with water and soap and draws lines with various needles and thicker ink with special attention not to cause too much pain. When artist finishes lines and cleans the skin again it is time to overlap the lines which results in a good hue of colors. When the tattoo is finished it is cleaned of blood again and covered in bandages. Bandages are removed 1 to 2 hours after the procedure and place is washed with cool water and an antiseptic soap that is not too strong. Water is patted dry without rubbing and place covered with antibacterial ointment. Healing will last from 1 to 3 weeks (depending on the health of the costumer) and place where the tattoo is should be concealed from the sun in that time.
When the needle with ink enters the skin it deposits the ink in the in the second layer of the skin – dermis. There pigment activates immune system of the body which sends macrophages which in turn eat the pigments of the ink. Some of the macrophage cells remove the pigment while other stay in the dermis along with the color. Other stay in dermal cells called fibroblasts that make the dermis along with nerves, blood vessels and collagen fibers. These fibroblasts don't fall of the skin when the epidermis (outer layer of the skin) regenerates but stay in the skin until they die and then are also absorbed (along with pigment inside them) by other, living fibroblasts which makes the tattoo permanent.