Most dermatologists view sebaceous glands as little more than oil-producing factories. However, mounting data has proven that in addition to producing sebum, these glands also play a role in both the immune and endocrine systems. Knowledge about the true function of the sebaceous glands is paving the way for new and novel medications to treat acne.
Sebaceous glands can be found throughout the body, but they are most dense on the face, ears, upper chest, and back. While sebaceous glands are typically associated with hair follicles, “free” sebaceous glands exist on mucosal surfaces. It is estimated that there can be anywhere from 2,500 to 6,000 sebaceous glands per square inch of skin.
A multi-functioning gland
The main function of sebaceous glands is to produce sebum that coats the outer skin layer, helping to keep it soft and supple. In patients with acne, higher amounts of sebum are produced compared to patients without acne. However, while sebum is a necessary component for the development of acne, it is more than simply a clog in the pipe. Qualitative differences in sebum drive the development of acne. The sebum of acne-prone patients has been demonstrated to have lower concentrations of linoleic acid, with higher concentrations of squalene. The qualitative differences play a pathogenic role in the development of acne. Linoleic acid is a building block for certain ceramides in the skin. Lack of linoleic acid contributes to the decreased ceramide levels that have been identified in acne patients. This ceramide deficiency is what is thought to contribute to the follicular hyperkeratinization within the follicles, since the skin barrier is defective. This causes a bottleneck that traps sebum within the follicle and leads to comedone development.
Did You Know?
It is estimated that there can be anywhere from 2,500 to 6,000 sebaceous glands per square inch of skin.
The increased squalene and triglycerides in sebum are also pathogenic. In a process known as lipid peroxidation, these fats promote inflammation when exposed to free radicals from environmental exposures.
C. acnes is a commensal organism that lives on all of our skin as part of our natural microbiome. C. acnes has been shown to directly stimulate sebaceous glands through toll-like receptor 2 (TLR2). This subsequently leads to the production of the pro-inflammatory mediators TNFα, IL-1α, and CXCL8 that promote the development of acne. They also produce antimicrobial peptides, including cathelicidin and Β-defensins. In this way, the sebaceous glands function as an independent immune organ.
Sebaceous glands are activated by testosterone and to a 30-times greater degree by dihydrotestosterone (DHT). It has been demonstrated that sebaceous glands produce 5-alpha-reductase, the enzyme that converts testosterone to DHT. In this way, sebaceous glands may be considered endocrine organs that are involved in hormonal activities that promote further activation of oil production.
Research Update: New Acne Risk Genes Identified
Researchers have identified 29 regions of the genome that influence acne. The research is published in Nature Communications.
Researchers analyzed nine genome-wide association study datasets from patients around the world. These studies involved scanning the whole genomes 20,165 people who had acne and 595,231 people who did not. The study identified 29 new genetic variants that are more common in people with acne. It also confirmed 14 of the 17 variants already known to be associated with the condition. This brings the total number of known variants to 46.
A number of genes were identified that are common in people with acne and are also linked to other skin and hair conditions. The team believes this will help to understand the causes of acne, which could be a mix of factors.
Function and Misfunction
While sebum production, follicular hyperkeratinization, C. acnes bacteria, and inflammation are all involved in the pathogenesis of acne, acne is ultimately a disease of the sebaceous gland itself. As we better understand the full function and misfunction of the sebaceous glands, we will have better therapeutic targets to treat acne by regulating both sebum production and inflammation in the skin.
For Further Reading
Szöllősi AG, et al. “Recent advances in the endocrinology of the sebaceous gland.” Dermatoendocrinol. 2017; 9(1): e1361576.
Ottaviani M, Camera E, Picardo M. Lipid Mediators in Acne. Mediators Inflamm. 2010; 2010: 858176.
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