Skin is Punctured
A needle is used to puncture the skin. The puncture goes below the epidermis (outer layer of the skin), to the dermis (second layer of skin). The needle must go to the second layer of skin to make the tattoo permanent. Otherwise, the tattoo would just disappear as the epidermis sloughed off.
Ink is Injected
Once the needle has punctured through to the dermis, a small drop of ink is injected into the skin. The ink is trapped in the dermis and will remain there throughout a person's entire life. This is because cells in the dermis are very stable and hold the ink in place.
Repeat the Process
The process of piercing the skin with a needle and injecting ink is repeated hundreds of times to form the desired design. Professional tattoo machines can puncture the skin and inject ink between 50 and 3,000 times per minute. When the design is complete, it is visible through the epidermis.