What are Sebaceous Glands?
Sebaceous glands are essential components of healthy skin. They produce and secrete sebum, which is responsible for moisturizing and protecting skin and hair. Damaged or malfunctioning sebaceous glands also play a central role in many dermatological conditions, such as acne vulgaris.
Sebaceous glands are clusters of specialized cells in the skin called sebocytes. Sebocytes are responsible for the synthesis and secretion of sebum. A complex blend of fatty acids, waxes, lipids and other molecules, sebum is responsible for moisturizing, lubricating and protecting the skin. Like adipose cells (fat cells), sebocytes accumulate large amounts of fats and lipids (different blends). But unlike adipose cells, sebocytes do not store energy. Rather, like true patriots, they sacrifice themselves for the greater good and undergo apoptosis (commit suicide). The death of the sebocyte releases the sebum stored within the cell and this sebum is exported through the follicle to the skin surface. Once there, the sebum then diffuses into the epidermis, moisturizing and protecting the tissue.
Sebaceous glands are composed of two main types of sebocyte cells (see second image) Peripheral Sebocyte Cells (PCs) line the outer edge of the sebaceous gland. Peripheral sebocytes are where the cellular reproduction happens, and from where the sebaceous gland originates and grows. Peripheral sebocytes accumulate relatively little sebum when compared to their more mature counterpart, Central Sebocyte Cells (CCs). Central sebocytes originate from proliferating peripheral sebocytes. As central sebocytes mature they migrate from the edges to the center of the sebaceous gland. During this process they begin to synthesize and accumulate large reserves of sebum, which they store in specialized storage structures inside the cell, called vacuoles. As they continue to mature, they migrate towards the hair follicle. When completely mature sebocytes reach the follicle opening, they undergo cellular suicide and spill their contents (sebum) into the follicle. This sebum then travels up the follicle to the surface of the skin, where it is essential for the maintenance of the epidermis.
The Role of Sebaceous Glands in Acne Vulgaris
Sebaceous glands can contribute to the development of acne in several ways. One of the most common problems faced by acne sufferers involves overactive sebaceous glands and/or sebaceous hyperplasia (enlarged sebaceous glands). These conditions can lead to an overproduction of sebum. Excess sebum can facilitate the growth of bacteria that contribute to acne symptoms, like Propionibacterium acnes. These bacteria can utilize sebum as a food source and large food supplies encourage bacterial growth. Excess sebum can also contribute to keratinized plugs that block the follicle and spur the development of inflammatory lesions. Sebum itself and the byproducts of its breakdown can be comedogenic themselves.
The Relationship Between Sebaceous Glands and Hormones
The well documented increase in acne rates that occurs during adolescence, particularly in males, is due largely to hormonal changes. The high levels of androgen hormones that begin circulating during male adolescence stimulate the growth of the sebaceous glands. Women with elevated androgen levels can also experience problems with androgen dependent sebaceous hyperplasia. Excessive levels of androgen hormones can be treated with androgen inhibitors, which suppress their effects. Sebaceous glands also appear to respond to non-androgen hormones, like Insulin Growth Factor (IGF), a hormone that has been loosely tied to milk consumption.
Sebaceous Glands and Retinoic Acid (Isotretinoin, Accutane, Retin-A, etc)
One of the most effective treatments for overactive or hyperplastic sebaceous glands are retinoic acids. Proliferating sebocytes have a receptor on their surface the binds to retinoic acid. When retinoic acid comes into contact with sebocytes, it initiates a cascade of changes that dramatically alter the growth pattern of sebocytes. Retinoic acid causes sebaceous glands to decrease in size and reduces their growth rate, resulting in dramatically decreased sebum production. In some cases, treatment with retinoic acid can decrease the production of sebum by up to 90%. Retinoic acid is not only active on sebocytes, it can also block the proliferation of other cells as well. The broad activity of retinoic acids on a diverse range of cells contributes to some of the side effects of retinoic acid treatment. The most troubling side effect of retinoic acid is its effect on the developing fetus. Retinoic acid dramatically disrupts normal embryonic development and leads to severe birth defects. For this reason, retinoic acid treatments are tightly controlled in many places, particularly for women.
Alternative Treatments for Sebaceous Hyperplasia
Emerging therapies that utilize light and laser treatments are becoming increasingly popular options for dealing with problematic sebaceous glands. Specialized photodynamic therapy (PDT) and diode lasers can be used to specifically target, damage and destroy sebaceous glands. While these treatments can be quite expensive and incompletely effective, their development offers the promise of additional treatments for acne sufferers.
References and Sources
Sebaceous Gland Lipids: Friend or Foe?
Smith, et al. 2008. For article abstract, click here.
Sebaceous Gland Receptors.
Zouboulis. 2009. For article abstract, click here.
Differentiation of the Sebaceous Gland.
Niemann. 2009. For article abstract, click here.
The Sebocyte Culture: A Model to Study the Pathophysiology of the Sebaceous Gland in Sebostasis, Seborrhoea and Acne.
Zouboulis, et al. 2008. For article abstract, click here.
The Role of Specific Retinoid Receptors in Sebocyte Growth and Differentiation in Culture
Kim, et al. 1999. For article abstract, click here.
Sebaceous Gland Lipids
Picardo, et al. 2009. For article abstract, click here.
Isotretinoin Revisited: Pluripotent Effects on Human Sebaceous Gland Cells
Zouboulis. 2006. For article abstract, click here.