Hair Embryology

During the 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 and seems to be directed by a collection of mesenchymal cells that eventually form the dermal (follicular) papilla.

The germ continues to grow deeper in the dermis under the guidance of the dermal papilla. It then 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]).

Sebaceous glands are absent in the palms and soles; apocrine glands develop only in certain body regions. The hair grows at a slant angle.

Melanocytes are scattered haphazardly in the primary epithelial bud.

Anatomy of the hair follicle.