What They Do
Depending on their location, there can be anywhere from 2,500 to 6,000 sebaceous glands per square inch. While most sebaceous glands are connected to a hair follicle, some open up directly to the surface of the skin. These include the meibomian glands of the eyelids and the Fordyce spots of the lips and genitals.
Sebaceous glands work in tandem with the sweat-producing eccrine glands to regulate body temperature. In hot conditions, the excreted sebum mixes with sweat to slow the rate of evaporation. In cold temperatures, the sebum will contain more lipids to shield the hair and skin from moisture that can facilitate heat loss.
In addition to maintaining moisture and regulating temperatures, sebum contains squalene and other substances that prevent bacteria, fungi, and other microorganisms from causing infection.
Sebaceous glands are first visible between weeks 13 and 16 of fetal development and emerge from the same stem cells that give rise to the outermost layer of skin, called the epidermis. Following birth, the activity of the glands will gradually decrease and become nearly inactive between the ages of two and six.
It is after this period that the production of sebum will steadily increase, reaching an apex during puberty as boys and girls both experience a sudden spike in male hormones (androgens). This overproduction, combined with the routine shedding of dead skin cells, can clog pores and lead to blackheads (open comedones), whiteheads (closed comedones), and pimples (acne).
Sebum production tends to slow by around the age of 20 and continues diminishing the older we get. As this occurs, the skin can become drier and lose elasticity. These changes, referred to sebostasis, tend to occur in tandem with decreases in androgen production.
The loss of moisture, combined with the depletion of collagen and keratin, can lead to characteristically dry skin (xerosis cutis) and brittle hair.
Role in Pimples
The condition most of us associate with the sebaceous glands is pimples. While the pores of the skin are great self-cleaning machines, any accumulation of dirt or debris can combine with sebum to create a glue-like compound that can seal the entryway.
Once blocked, bacteria like Staphylococcus aureus and Propionibacterium acnes can begin to multiply and thrive, leading to the development of a pus-filled bump we recognize as a pimple. The colonization of bacteria will further trigger an immune response, leading to inflammation as the body tries to control the infection.
Pimples are medically referred to as acne vulgaris. Those that are severe and consolidate into boil-like pustules are known as cystic