The cells in the epidermis of your skin - the outer layer - are constantly renewing themselves (a lot more quickly than once every 10 years, BTW). But, there are several cells which do not (normally) divide in the adult body. Nerve cells, for example, have extremely limited regeneration potential. The best example, however, is the lens fibre cells which compose the bulk of your eye lens: the primary fibre cells in the core of the lens were laid down 7 months before you were born, and remain un-growing for your entire life. > "how come our tattoos and scars remain?" Tattoos are not *inside* any cell: the tattoo ink is deposited into the skin dermis, the layer underneath the epidermis. Cells in your skin ARE constantly dividing and being shed from the surface, but this happens in the epidermis, and does not effect the tattoo in the dermis below. Obviously, if you receive a penetrating injury to the tattoo, which damages the dermis, then some of the tattoo will be displaced by scar tissue. Tattoos also blur and fade with time, as the ink is photo-bleached by UV light from the sun, and as the dye "leaks" slowly into surrounding tissues. Scarring is not a change to the cells themselves, it is a larger-scale change to the structure of a tissue. When a tissue is damaged, the cells divide to repair the damage, but this repair might not be perfect - different cells and ECM proteins might be deposited, and the 3D arrangement of the newly-produced cells might not be the same as the original tissue: this is a "scar".