Human skin replaces itself approximately once every 27 days, according to WebMD. The process of skin renewal occurs through exfoliation.
The external layer of the human skin is called the epidermis and it replaces itself approximately every 27 days through shedding, which is known as exfoliation. Only this outer or surface layer of skin is replaced during the exfoliation process. The dermis and hypodermis, which are the deeper skin tissue layers beneath the epidermis, do not experience exfoliation. Scars to the body often affect these deeper layers and since they do not get replaced, the scars remain. Additionally, tattoo inks typically affect both the epidermis and the dermis and as such do not disappear with the skin's natural exfoliation.