Human skin is made up of two principal parts: the epidermis and the dermis. The outer, thinner, epidermis consists of four or five cell layers and is designed to shed cells and be replaced. The inner dermis is made up of two portions: the upper, papillary region and the reticular region. Within the lower regions there are long lasting phagocytic connective tissue cells that can remain almost completely unchanged for an entire lifetime. Tattoos are made by inserting ink into the deepest layers of the dermis portion of the skin, including these long-lived cells. That is why tattoos can last a lifetime.