Vellus hair – fine, hypopigmented hair in truncal/extremities
Terminal hair – scalp, face, groin, axilla
Same hair follicles can produce both terminal and vellus hair at different phases of life.
third month of gestation, the epithelial primary hair germs develop in the eyebrow region and scalp.
Subsequently, hair development continues in a cephalocaudal direction.
The primary hair germ begins as an epithelial bud that protrudes into the dermis -directed by a collection of mesenchymal cells that eventually form the dermal (follicular) papilla.
Acquires multiple epithelial buds that grow transversely and differentiate into the many components of the primary hair follicle (ie, sebaceous gland and duct, apocrine gland and duct, attachment point of the erector pili muscle [bulge region]).