Acne is in part a bacterial disease. When it comes to acne, the bacteria in question is a specific type called P. acnes.
Scientists found that P. acnes may contribute to the formation of clogged pores, cause irritation inside a pore once it is clogged, and cause a pimple to become more inflamed, red, and sore.
However, there are multiple P. acnes strains which are present in different amounts in the skin of acne-prone people. Here's where the deep science comes in: For example, P. acnes type IA1 is present in higher amounts in acne-prone skin than in healthy skin. Further, preliminary research suggests that this strain demonstrates a slightly altered effect on the immune system when compared with other types, and consequently likely contributes to acne development differently.
Scientists will need to perform further research to better characterize the differences among the types of P. acnes as well as other bacterial species, such as Staphylococcus and Klebsiella, to determine how each affects acne development.
Clogged pores form through the accumulation of skin cells and sebum (skin oil) that clog a hair follicle (pore). If the contents of the follicle are unable to escape the clog, they continue to build up until the follicular wall ruptures. This rupture causes inflammation that forms inflammatory acne, i.e., papules and pustules—the red, inflamed lesions people refer to as “pimples” or “zits.” Many factors, including overproduction of sebum, skin cell overgrowth, hormones, and bacteria, contribute to the formation of these inflammatory acne lesions. Scientists have been interested especially in identifying the role of bacteria and bacterial strains in acne development. It became clear that acne-prone and healthy individuals carry different bacteria and bacterial strains in their skin, only some of which may contribute to the formation of acne.
Role of P. acnes in Acne Development
Propionibacterium acnes (P. acnes) is a single-cell bacterium that is present in both healthy and acne-prone skin. It survives using sebum as a source of nutrients, and therefore thrives in clogged pores, where sebum is abundant. Although scientists previously thought P. acnes was the main cause of acne, recent research found that it is not present in all acne lesions, and therefore is likely to play only a secondary role in acne formation.1 Researchers now believe that P. acnes contributes to the worsening of previously formed acne lesions in three main ways.
- Producing proteins that adhere to the follicular wall. Once the bacterium is stuck to the follicle wall, it can better survive and reproduce.2–3
- Creating and releasing certain proteins that assist in the degradation of the follicular wall, contributing to its rupture and ensuing inflammation.2–3
- Stimulating the immune response by triggering the release of inflammatory molecules, which results in inflammation. One main class of inflammatory molecules that P. acnes releases is called CAMP (Christie, Atkins, Munch, Peterson) factors. CAMP factors are able to puncture immune cells, resulting in immune cell death, toxicity, and release of additional inflammatory molecules that worsen inflammation.2–4
Bacterial Strains of P. acnes and Acne Development
Scientists classify bacteria of the same species into small subgroups called strains. To group bacteria into strains, scientists sequence the bacterial genome and sort groups of bacteria with at least 95% identical DNA. There are about 100 strains of P. acnes that scientists further classified into three types: type I, type II, and type III. Type I contains the additional four subgroups, type IA1, type IA2, type IB, and type IC.5 Scientists have performed four independent studies to identify if the different strains present in the skin influence acne development differently. All four studies found that type IA1 is more abundant in acne-prone skin than in healthy skin.6–9
Further, one of the studies found that type II strains were not present in the acne skin samples, and another showed that the same was true of type III strains. But in both studies, these strain types made up around 20% of all bacteria in the healthy skin samples.7,9
With the knowledge that type IA1 is more abundant in acne-prone skin than in healthy skin, scientists have attempted to classify if this particular type of P. acnes contributes to acne development in a special way. Researchers performed three studies to identify potential disparities in acne-promoting proteins or other factors among the various P. acnes types.
Expand to read details of studies
A 2005 study found that P. acnes type IA1 produced much lower levels of CAMP-1 than types IB and II, but higher levels of CAMP-2 than type II. Although it remains unclear how this affects the inflammatory response, this study concluded that different P. acnes types could provoke unique immune responses.10
A 2010 study discovered that P. acnes type IA1 produced more follicular adhesion proteins, which likely helps the bacteria stick better to the follicular wall, thus promoting clogged pores.11
A 2013 study examined the immune system response to P. acnes in laboratory-grown human cells. They used their data to order the P. acnes types by strongest immune response (type III) to weakest immune response (type IB). They found that the order of immune system response from strongest to weakest is type III, II, IC, IA1, and IB. Further, the scientists found that each P. acnes type stimulated the release of different inflammatory molecules called cytokines, which in theory could stimulate unique immune system responses.12
Although scientists have not yet confirmed how the differences identified in these studies contribute to acne development, it is clear that acne-prone patients retain more type IA1P. acnes on their skin and that this type stimulates the immune system in different ways than the other P. types. Researchers need to perform more research to understand how these differences affect acne development.
Other Bacterial Species in Acne Development
Although scientists have focused their acne development research on P. acnes, there is a variety of bacterial species present on the skin that also may affect acne formation.
- Researchers found that the presence of Staphylococcus epidermidis (S. epidermidis) is increased by 70% in acne-prone skin. Further, research shows that S. epidermidis secretes factors that can worsen follicular clogging.
- It also was noted that Staphylococcus aureus (S. aureus) is present at higher levels in many skin disorders, including acne. Scientists believe that it may produce proteins that aid in follicular wall rupture.
- In addition, researchers found Staphylococcus pyogenes (S. pyogenes) in the oropharynx (region including the back of the throat and tongue) in acne-prone individuals but not healthy individuals. It is not yet clear how bacteria present in the oropharynx affects the development of acne.
- Klebsiella pneumoniae (K. pneumoniae) also was found in acne lesions, but not in healthy skin. This was the only acne-associated bacteria exclusive to acne lesions.
- Streptococcus agalactiae (S. agalactiae) produces factors that are similar to those of P. acnes and is assumed to be involved in acne development.1
The research into the specifics of various bacteria strains is an exciting area of exploration. However, it is just getting underway. Scientists have performed scarce research examining these bacterial strains’ roles in acne development, and therefore researchers must perform more studies to confirm these associations.
The Bottom Line
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