The structure consisting of hair, hair follicle, arrector pili muscles, and sebaceous gland is an epidermal invagination known as a "pilosebaceous unit".
Processes affected include pubertal growth, sebaceous gland oil production, and sexuality (especially in fetal development).
There are two types of sebaceous gland, those connected to hair follicles, in "pilosebaceous units", and those that exist independently.
Sebum is a sticky oil-like substance which is produced from the sebaceous gland.
Within the latter type, there are hairs in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle.
Each strand of vellus hair is usually less than 2 mm (1/13 inch) long and the follicle is not connected to a sebaceous gland.
Sebum is produced in a holocrine process, in which cells within the sebaceous gland disintegrate as they release the sebum.
Warthogs have two facial glands the tusk gland and the sebaceous gland.
