A hair follicle is a part of the skin that grows hair by cramping old cells tightly. Attached to the follicle is a sebaceous gland, a tiny sebum-producing gland found everywhere except on the palms, lips and soles of the feet. The thicker the density of the hair, the more the number of sebaceous glands that are found.
Also attached to the follicle is a tiny bundle of muscle fiber called the arrector pili that is responsible for causing the follicle lissis to become more perpendicular to the surface of the skin, and causing the follicle to protrude slightly above the surrounding skin (piloerection) and a pore encased with skin oil. This process results in goose bumps (or goose flesh). Stem cells are located at the junction of the erector and the follicle, and are principally responsible for the ongoing hair production during a process known as the Anagen stage.
The average growth rate of healthy hair follicles on the scalp is half an inch per month.