* Adapted with permission from a virtual presentation given during the 7th Anti-Ageing Skin Care Conference, London, Nov. 3-5, 2020.
Millions of native microbes populate skin, the most relatively abundant species being Cutibacterium acnes (formerly Propionibacterium acnes).1 Most historical research of C. acnes focused on its association with acne, giving a poor reputation. However, its high relative abundance suggests it has co-evolved with humans and therefore, its presence may confer skin benefits. This hypothesis is strengthened by the exclusive niche that C. acnes inhabits—it is nearly the sole inhabitant of the sebaceous hair follicle. And while the host can, with an arsenal of antimicrobial peptides, control what microbes live in this niche, C. acnes is the one microbe allowed to inhabit this space. Why?
The present discussion explores C. acnes and its mutualistic role in skin health. The authors also propose its utility as a probiotic to address skin deficiencies as they change from adolescence to adulthood.2 While the technology to support this approach is still being developed, the research suggests it could be a path forward for skin concerns as they change throughout life.
C. acnes Potential
As noted, past research has focused mainly on the negative side effects of C. acnes, implicated in the chronic skin disease Acne vulgaris. And like many other skin commensal organisms, C. acnes can become an opportunistic pathogen. However, the question of why this bacterium is so abundant on the skin has long been overlooked.
In more recent years, it has become clear that C. acnes is contributing to skin health in many ways, for example by:
• supporting skin’s defenses both directly, by producing the antimicrobial peptide cutimycin,3 and indirectly with fermentation products;4
• stimulating autophagy,5 an essential cellular process involved in everything from skin aging6 to cancer;7
• inducing sebum production through its metabolites;8
• ameliorating unusual cases of skin itch;9 and
• acting as an important pillar in skin’s antioxidant defense.10, 11
With new insights mainly driven by next-generation sequencing, the view of C. acnes has changed dramatically. The species is now recognized as a sentinel that contributes actively to skin homeostasis and promotes healthy skin aging. A similar transformation of scientific opinion previously occurred for Staphylococcus epidermidis. This microbe was extensively targeted for its ability to form biofilms on surgical implants, causing difficult-to-treat infections, but today, together with C. acnes, S. epidermidis is regarded as a commensal entity.12
However, the simple addition of “good” bacteria such as C. acnes is not a one-size-fits-all answer to skin problems. A tailored approach, carefully modulating the C. acnes community and responding to current skin needs, is required. Take sebum, for example. As noted, C. acnes is a strong modulator of sebum production, and sebum is a key component of the skin’s acid mantle. While teenagers produce higher amounts of sebum, resulting in a shiny appearance and oily skin feel, sebum secretion is reduced later in life.13 Therefore, for teenagers, adding a C. acnes strain to skin that increases sebum production would generally be undesirable, whereas in mature skin such a strain might be embraced.
How did we happen to overlook the benefits of C. acnes for such a long time? There are two main reasons. The first is a generic one: it is easier to confirm that a microbial species causes a disease rather than supports health. As such, most research conducted in this field has related to specific diseases and not to healthy skin states.
The second reason is that not all C. acnes strains are the same; in fact, they are quite different—and since scientists have typically referred to disease-focused research, as noted above, they have been more prone to study the “bad” C. acnes strains. Occasionally, a healthy control has been assessed but usually to identify the microbial features related to the disease. Features that could contribute toward skin health were rarely the focus until the Human Microbiome Project Consortium expanded our understanding of the large impact the microbiome has on human health.14
Unfortunately, not even next-generation sequencing has ensured we can truly distinguish all C. acnes strains.
- Byrd, A.L., Belkaid, Y. and Segre, J.A. (2018). The human skin microbiome. Available at: https://doi.org/10.1038/nrmicro.2017.157
- Rozas, M., Hart de Ruijter, A. ... Brillet, F., et al. (2021). From dysbiosis to healthy skin: Major contributions of Cutibacterium acnes to skin homeostasis. Available at: https://doi.org/10.3390/microorganisms9030628
- Claesen, J., Spagnolo, J.B., ... Lemon, K.P., et al. (2020). A Cutibacterium acnes antibiotic modulates human skin microbiota composition in hair follicles. Available at: https://doi.org/10.1126/scitranslmed.aay5445
- Shu, M., Wang, Y., Yu, J., Kuo, S., Coda, A., Jiang, Y., Gallo, R.L. and Huang, C.-M. (2013). Fermentation of Propionibacterium acnes, a commensal bacterium in the human skin microbiome, as skin probiotics against methicillin-resistant Staphylococcus aureus. Available at: https://doi.org/10.1371/journal.pone.0055380
- Megyeri, K., Orosz, L., ... Kemény, L., et al. (2018). Propionibacterium acnes induces autophagy in keratinocytes: Involvement of multiple mechanisms. Available at: https://doi.org/10.1016/j.jid.2017.11.018
- Eckhart, L., Tschachler, E. and Gruber, F. (2019). Autophagic control of skin aging. Available at: https://doi.org/10.3389/fcell.2019.00143
- Dikic, I. and Elazar, Z. (2018). Mechanism and medical implications of mammalian autophagy. Available at: https://doi.org/10.1038/s41580-018-0003-4
- Iinuma, K., Sato, T., ... Ito, A., et al. (2009). Involvement of Propionibacterium acnes in the augmentation of lipogenesis in hamster sebaceous glands in vivo and in vitro. Available at: https://doi.org/10.1038/jid.2009.46
- Keshari, S., Wang, Y., ... Huang, C.-M., et al. (2020). Skin Cutibacterium acnes mediates fermentation to suppress the calcium phosphate-induced itching: A butyric acid derivative with potential for Uremic Pruritus. Available at: https://doi.org/10.3390/jcm9020312
- Allhorn, M., Arve, S., Brüggemann, H. and Lood, R. (2016). A novel enzyme with antioxidant capacity produced by the ubiquitous skin colonizer Propionibacterium acnes. Available at: https://doi.org/10.1038/srep36412
- Andersson, T., Bergdahl, G.E., ... Lood, R., et al. (2019). Common skin bacteria protect their host from oxidative stress through secreted antioxidant RoxP. Available at: https://doi.org/10.1038/s41598-019-40471-3
- Fournière, M., Latire, T., Souak, D., Feuilloley, M.G.J. and Bedoux, G. (2020). Staphylococcus epidermidis and Cutibacterium acnes: Two major sentinels of skin microbiota and the influence of cosmetics. Available at: https://doi.org/10.3390/microorganisms8111752
- Pochi, P.E., Strauss, J.S. and Downing, D.T. (1979). Age-related changes in sebaceous gland activity. Available at: https://doi.org/10.1111/1523-1747.ep12532792
- The Human Microbiome Project Consortium. (2012). Structure, function and diversity of the healthy human microbiome. Available at: https://doi.org/10.1038/nature11234