Sebaceous glands:

Sebaceous glands plays an important role in the formation of acne hence it is important to understand the structure and function of this gland. Sebaceous glands are small, sac-shaped oil-producing glands present in the dermis layer of the skin in mammals. These glands are also called Holocrine Glands because the secretion (i.e. sebum) of these glands is formed by the complete destruction of the cells. These glands are found over the entire surface of the body except the palms, soles, and dorsum of the feet. They are highly concentrated on the face and the scalp where they are the sites of origin of acne.

Sebaceous glands are also found in non-haired areas (glabrous skin) of eyelids, penis, labia minor and the nipples. Here, the sebum traverses ducts which terminate in sweat pores on the surface of the skin. Pores on an average ranges in size from 50 to 80 μm.

The inner surface of the lip and the buccal surface of the cheek also contain ectopic sebaceous glands commonly known as Fordyce’s spots or Fordyce granules. These occur as yellowish circular dots that form clusters. Eighty percent of the population shows the presence of Fordyce granules.

Specialized form of sebaceous glands is present at the rim of the eyelids called as Meibomian glands. They secrete sebum into the tears coating the eyes to slow evaporation.

Function of Sebaceous glands:
The main function of sebaceous gland is to secrete an oily substance called as sebum. The human sebum is composed of 41% triglycerides, 16% free fatty acids, 25% wax esters and cholesterol, 12% squalene. Sebum lubricates the skin to protect against friction and controls moisture loss from the epidermis. The sebum also protects against fungal and bacterial infections of the skin due to its contents of free fatty acids.
The sebaceous glands are usually attached to the hair follicles and secrete sebum that drains into the follicular duct and eventually on the surface of the skin. The structure consisting of hair, hair follicle, erector pili muscles, and sebaceous gland is known as a pilosebaceous unit. The excess production of sebum blocks the follicular pores. Due to the accumulation of sebum bacteria like Propionibacterium acne starts growing and hence leads to the formation of different types of acne. The production of sebum is under hormonal control, specifically androgen during adolescence which varies from person to person but the secretion of sebum is a continuous process.