Here's a breakdown:
* Epidermis: This is the outer layer of skin that you can see and touch. It constantly sheds and regenerates. If tattoo ink were only in the epidermis, it would disappear quickly.
* Dermis: This is the deeper layer of skin that contains blood vessels, nerves, hair follicles, and connective tissue. Tattoo needles penetrate the epidermis and deposit the ink into the dermis. The dermis is more stable, which is why tattoos are permanent (or at least very long-lasting).
* Hypodermis: This is the layer of tissue beneath the dermis that contains fat and larger blood vessels.
So, the tattoo machine uses needles to repeatedly puncture the skin, delivering small droplets of ink into the dermis. The body's immune system responds to this by trying to clear away the foreign substance (the ink), but some of the ink becomes trapped within the cells of the dermis, and some is encapsulated by collagen fibers. This is what makes the tattoo visible through the epidermis.