Medical Literature Library

Understanding the Faceted Nature of the Cutibacterium acnes Species

When we talk about probiotics, we often refer to what species or number of species are contained in that probiotic product. But did you know that not all microbes within a species are the same? An example of this is when we hear about bacteria becoming antibiotic resistant, we're talking about different strains within the same species. In fact, scientists are discovering more and more about how there are benefits to using certain strains of skin-relevant probiotic bacteria species over other strains in the same species.

Significant differences between strains of a species are a common phenomenon and is the case with the bacteria species Cutibacterium acnes. This species lives on everyone's skin, but many strains have different characteristics. Scientists have even revised the naming convention for the major groups within this species, dividing them into three subspecies: 

  1. Cutibacterium acnes subspecies acnes
  2. Cutibacterium acnes subspecies defendens
  3. Cutibacterium acnes subspecies elongatum

These groupings are based on significant genetic and phenotypica differences between them, differences that have been shown to factor into whether particular strains within each group might be either pathogenic or protective. Either way, being the most prolific bacteria on healthy human skin, what strains of this species that lives on your skin can make a big difference in your health and beauty.

What we now know about C. acnes

While for a long while it was thought that C. acnes was a pathogen that directly caused acne, it has been shown in the last decade that everyone on Earth has large amounts of this species on their skin, thus it is not possible that the simple presence of the species causes skin issues. Though some strains are known to be more associated with acne, it is difficult to prove that these strains cause acne directly. Research has shown that the presence of other bacteria and fungi and how the skin and immune system respond to them are equally important in determining the cause of acne. Additionally, multiple studies have shown that acne-prone skin has a relative decrease in C. acnes and a relative increase in other bacteria and fungi, including Staphylococcus epidermidis, which can contribute to pore blockage through the production of biofilms and encouragement of hyperkeratinization via inflammation. However, many publications speculate that S. epidermis helps control C. acnes to prevent acne, which doesn't seem to make sense given the data showing that follicles of those with acne tend to have less C. acnes and more S. epidermidis.

The study of immune cells from different individuals has shown that their reactions to the same pathogenic C. acnes can vary. While the immune systems of healthy individuals and those with acne had increased inflammatory signals, the cells of those with acne could not produce enough anti-inflammatory signals to balance this increase. This suggests that the immune cells of those with acne are more prone to inflammation, which might explain why two people with the same C. acnes strain on their skin can have different outcomes, with only some developing acne. Additionally, this is made more complicated as most studies don't consider the variable of the human immune system as well as the interaction of bacterial and fungal strains on the skin, and the implications of such interactions.

There is no conclusive evidence that the presence of any given strain of C. acnes alone is enough to cause disease. The level of skin biome balance as well as a properly functioning immune system is crucial in determining whether the strains will cause skin problems. This is one reason why acne is not known to be communicable. So, while it's true that some strains of C. acnes can be a factor in acne, it's not as simple as just blaming it for the problem. There are many other factors at play that scientists are still trying to understand. As we know, the skin biome is a complex system. Indeed, there is quite a bit of emerging evidence that there are also protective strains of C. acnes that play a critical role in maintaining skin health and beauty. These strains secrete substances that protect the skin from pathogens and environmental stressors, such as free radicals.

Differences between Disease-associated and Protective C. acnes Strains

The presence of different genes or variations in gene expression can make some strains of C. acnes more or less prone to being associated with the disease. For example, disease-associated C. acnes strains produce more gene products for CAMP2, CAMP3, and CAMP5, while protective strains produce more CAMP1. These differences can result in different effects on the human host, as some of these gene products can cause inflammation.

Pathogenic strains have been shown to secrete inflammatory substances and have been used in scientific studies to cause inflammation intentionally. However, some strains of C. acnes have been found to stop inflammation instead of causing it. One such strain is XYCW1 as described by Rhee et al. which is a strain from the subspecies C. acnes subspecies defendens, which was discovered to have beneficial effects on skin during a study conducted by our research team. In addition to these genetic differences, protective strains tend to have a CRISPR element, a type of bacterial immune system, while pathogenic strains most often do not. The absence of this element allows for the integration of genetic material from phages and other pathogenic strains, which can lead to the emergence of pathogenic traits.

Overall, these findings suggest that certain C. acnes strains might not simply be commensal but might even have a symbiotic relationship with their human hosts.

The Protective Role of C. acnes Strains on Skin Health

Some of the key benefits that protective strains of C. acnes bring to the skin include:

  • Propionic acid:This substance is a targeted antimicrobial that actively suppresses the growth of pathogens like S. aureus, including MRSA. It also has broad-spectrum antimicrobial activity against Escherichia coli and Candida albicans. In addition, propionic acid inhibits biofilm formation, is a tyrosinase inhibitor, and its salt form is a potent antioxidant.
  • RoxP:This is a potent antioxidant that is specific to C. acnes and has been suggested to be as potent as Vitamin C or Vitamin E. The big difference being that C. acnes secretes RoxP all the time, leading to all day long antioxidant protection (as long as you don't over wash).
  • Cutimycin:This is an antibiotic that is produced by C. acnes and targets Staphylococcus species, including S. aureus and S. epidermidis.
  • Reduced porphyrins:Disease-associated strains of C. acnes are known for producing porphyrins (which can be inflammatory), but protective strains tend to secrete little to none.

The interplay between human cells and the skin microbiome is complex and depends on both the environment and the mixture of microbial strains present. C. acnes is ubiquitous on the skin of the entire human population, and the benefits of the protective strains of C. acnes are on par with some of the best skin care products. It's important to recognize the distinction between disease-associated and protective strains of C. acnes to better understand the role of this species in skin health and help you understand how to improve your skin microbiome.

In conclusion, the role of C. acnes in skin health is complex and multifaceted. While it has been traditionally associated with disease, research has shown that certain strains of C. acnes can actually be beneficial, maybe critical, to skin health and beauty. These protective strains produce substances that can suppress the growth of pathogens, act as antioxidants, and inhibit inflammation. Understanding the differences between disease-associated and protective strains of C. acnes is critical in our quest for a healthy skin biome. By recognizing the benefits of protective strains, we can shift our focus from simply trying to eliminate all C. acnes, to fostering a healthy balance of this important species on our skin.


Thomas Hitchcock, Ph.D., is the Chief Science Officer for Crown Laboratories, where he oversees clinical development, medical affairs, biological sciences, product development, and research and development for the privately held, fully integrated global company dedicated to developing and providing a diverse portfolio of safe and effective scientific solutions for life-long healthy skin. Dr. Hitchcock is a formally trained scientist with expertise in molecular genetics, microbiology, and dermatology. He has 20+ years of research experience, including basic science, preclinical, and clinical research across several therapeutic areas. He has also been issued patents on his inventions in aesthetic medicine, dermatology, and microbiology. Dr. Hitchcock lectures and presents his research internationally. His work has been published in notable journals such as the “Journal of Biological Chemistry,” “Annals of the New York Academy of Sciences,” “Clinics in Plastic Surgery and Nature,” “Journal of Cosmetic Dermatology,” “Aesthetics Surgery Journal,” “Nucleic Acid Research,” and “Cell Transplantation.” He is also the co-author of the book “Rebooting the Biome”.