Sebaceous gland

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Structure and layers of the skin.

Sebaceous glands are small, sacculated glands situated within the dermal layer of the skin, typically connected to hair follicles. They produce and secrete an oily or greasy substance primarily composed of fats called sebum. This substance functions to soften, moisturize and lubricate both the hair and the skin, contributing to overall skin health and maintenance. 

Sebaceous glands emerge from the hair follicle's external root sheath, often as multiples per follicle. They consist of a secretory portion (composed of sebocytes) and a short excretory duct
that empties into the pilary canal/infundibulum of the hair follicle. The arrector pili muscle accompanies the sebaceous gland, aiding in the secretion and discharge of its contents into the infundibulum. Hence, a sebaceous gland and related arrector pili muscle are often collectively referred to as pilosebacous unit. 

The sebum that is produced is a product of holocrine secretion. This means that the entire cell produces and becomes filled with the fatty secretory product while simultaneously undergoing programmed cell death or apoptosis. Both secretory product and cell debris are then discharged as sebum into the piliary canal/infundibulum of a hair follicle. New cells are produced by mitosis of the basal cells at the periphery of the gland.