Epidermal keratinocytes comprise 90 % of all cells found in the epidermis the outermost layer of skin. They produce keratin the intermediate filament largely responsible for skins barrier function. Through their interactions with epidermal melanocytes keratinocytes obtain melanin and store it as a means of protection from UV radiation.HEK provide an excellent model system to study many aspects of epithelial function and disease particularly those related to skin biology and toxicology as well as HPV infection. When grown on inserts and provided with the liquid/air interface HEK can differentiate into a stratified squamous epithelium and serve as a more physiological 3D tissue model for in vitro studies.