Stem cells in the skin. Stem cells in the basal layer of the interfollicular epidermis replenish the multilayered epithelium (spinous, granular, clear, and cornified layers). The hair follicle composes the cycling (epithelial hair germ cell) and noncycling (bulge, isthmus, infundibulum, and sebaceous gland) portion. The bulge is separated into upper, middle, and lower portions. Hair follicle stem cells in the bulge replenish hair, but also the sebaceous gland and interfollicular epidermis in response to injury.