Hair is formed from the protein keratin and is pushed up by growth from the bulb at the base of the follicle. When hair follicles regress, epithelial cells are removed by apoptosis. Neighbouring epithelial cells clean up the mess by phagocytosis.
Epithelial stem cells in the skin are multipotent. They are responsible for generating the cells of the hair follicle, the epidermis and the sweat (sebaceous) gland. Stem cells associated with hair follicles are responsible for maintaining and regenerating them.
Hair growth occurs in a number of phases. The first phase is active growth. After the active growth phase the hair follicles stop producing hair and go through a process of regression. When hair follicles regress, the epithelial cells which make it are slowly destroyed (apoptosis). Neighbouring epithelial cells then clean up the mess by phagocytosis. Stem cells are left at the end in case the follicle needs to regenerate.
This image was inspired by research by Valentina Greco.