Electric tattoo needles create semi-permanent designs by rapidly injecting ink into the second layer of skin, known as the dermis. Each penetration is roughly 1 millimeter in depth, and the ink is deposited into the tiny punctures. Tattoo artists use insoluble ink that does not dissolve, and special tattoo needles can make up to 3,000 injections per minute, according to How Stuff Works.
Tattoo needles must penetrate beyond the first layer of skin, or epidermis, because these cells are continually shed and replaced. Skilled artists use different needle sizes for outlining, shading and coloring tattoos. They learn how to control the needle to avoid pushing too far into the skin and causing bleeding. If the needle does not penetrate far enough, the tattoo can lack visual consistency.
Individuals who scar easily or suffer from bleeding disorders are often advised against getting tattoos. With every puncture, the needle is technically leaving a wound, so new tattoos must be washed and treated with ointment to heal the skin properly and prevent infection.
Since tattoo artists and their customers are exposed to blood, tattoo shops must follow safety procedures to sterilize their equipment and dispose of hazardous material. For example, reputable tattoo shops sterilize reusable equipment with autoclave machines, which use steam, heat and pressure to eliminate bacterial organisms. They also follow federal standards for handling blood, known as universal precautions, in order to avoid spreading diseases, such as hepatitis.