A stratified epithelium that surrounds the hair follicle that merges proximally with the basal layer of the interfollicular epidermis and distally with the hair bulb. [ https://github.com/obophenotype/mouse-anatomy-ontology/issues/56 http://www.keratin.com/aa/aa022.shtml https://doi.org/10.1016/j.cub.2008.12.005 ]