Hair follicles that grow together naturally as a group. They share the same blood supply, nerves and muscle (arrector pilorum). The follicular unit of the adult human scalp consists of 1-4, and occasionally 5, terminal hair follicles, 1, or rarely 2, vellus follicles and is surrounded by a band of collagen. In a follicular unit hair transplant, only intact follicular units are used in the procedure.