Sebaceous Glands

Sebaceous Gland High Magnification

Sebaceous glands produce and secrete sebum, which is responsible for moisturizing and protecting skin and hair. Sebaceous glands are essential components of healthy skin. Damaged or malfunctioning sebaceous glands contribute to many dermatological conditions, including acne vulgaris.

Structure of the Sebaceous Glands

Hair Follicle, Sebaceous Glands and Sebum (Wikipedia)
Hair Follicle, Sebaceous Glands and Sebum (Wikipedia)

Sebaceous glands are clusters of specialized cells in the skin. These specialized cells are called sebocytes. Sebocytes are responsible for the synthesis and secretion of sebum. Sebum is a complex blend of fatty acids, waxes, lipids and other molecules that are responsible for moisturizing, lubricating and protecting the skin.

Sebocytes are similar to adipose cells (fat cells) because they accumulate large amounts of fats and lipids. 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 hair follicle to the skin surface. Once at the skin surface, the sebum then diffuses into the epidermis where it moisturizes and protects the tissue.

Sebaceous Gland Magnified and Sebum Lipids Labeled with Fluorescent Dye (Smith-and-Zouboulis)
Sebaceous Gland Magnified and Sebum Lipids Labeled with Fluorescent Dye (Smith-and-Zouboulis)

Sebaceous glands are composed of two main types of sebocyte cells – Peripheral Sebocytes and Central Sebocytes. 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 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.

Sebaceous Glands and Acne

Sebaceous Hyperplasia
Sebaceous Hyperplasia

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 sebaceous hyperplasia (enlarged sebaceous glands). These conditions can lead to an overproduction of sebum. Excess sebum can facilitate the growth of bacteria (eg. Propionibacterium acnes) that contribute to acne symptoms. These bacteria can utilize sebum as a food source and large food supplies encourage bacterial growth.

Excess sebum production by overactive sebaceous glands can also cause the formation keratinized plugs (clogged pores) that block the follicle and spur the development of inflammatory lesions. Sebum itself and the byproducts of its breakdown can also be comedogenic themselves.

Sebaceous Glands and Hormones

Testosterone is an Androgen Hormone
Testosterone is an Androgen Hormone

Androgen (male) hormones stimulate the growth and activity of the sebaceous glands. Hormonal changes are largely responsible for the well documented increase in acne rates that occurs during adolescence, particularly among males. 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 Retinoids

Retinoids are a class of acne treatment that can reduce the activity of sebaceous glands. When retinoids comes into contact with sebocytes, it initiates a cascade of changes that dramatically alter the growth pattern of sebocytes. Retinoids causes sebaceous glands to decrease in size and reduces their growth rate, resulting in dramatically decreased sebum production. In some cases, treatment with retinoids can decrease the production of sebum by up to 90%.

Isotretinoin (Roaccutane) 20mg Capsules
Isotretinoin (Roaccutane)

Retinoids can also affect the proliferation of other types of cells. The broad activity of retinoids on a diverse range of cells contributes to some of their potentiatl side effects. The most dangerous side effect of retinoid treatment is potential damage to a developing fetus. Retinoids dramatically disrupt normal embryonic development and leads to severe birth defects. For this reason, oral retinoids (eg. Isotretinoin/Accutane) are tightly controlled in many countries, particularly for women.

Retinoids are available in both oral and topical formulations. Isotretinoin (Accutane) is generally the only retinoid available as an oral treatment. Isotretinoin, Tretinoin, Adapalene and Tazarotene are all retinoids that are available as topical treatments. Topical retinoids tend to be less effective acne treatments than oral retinoids, but have fewer side effects.

Additional Treatments for Sebaceous Hyperplasia

ALA Pretreatment for Photodymanic Therapy of Sebaceous Hyperplasia
ALA Pretreatment for Photodymanic Therapy of 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

Sebaceous Gland Lipids: Friend or Foe? Smith, et al. 2008.
Sebaceous Gland Receptors. Zouboulis. 2009.
Differentiation of the Sebaceous Gland. Niemann. 2009.
The Sebocyte Culture: A Model to Study the Pathophysiology of the Sebaceous Gland in Sebostasis, Seborrhoea and Acne. Zouboulis, et al. 2008.
The Role of Specific Retinoid Receptors in Sebocyte Growth and Differentiation in Culture Kim, et al. 1999.
Sebaceous Gland Lipids Picardo, et al. 2009.
Isotretinoin Revisited: Pluripotent Effects on Human Sebaceous Gland Cells Zouboulis. 2006.