Acne vulgaris remains one of the most common chronic inflammatory skin disorders worldwide, especially among adolescents and young adults. The condition appears as blackheads, whiteheads, papules, pustules, and in severe cases, nodules that can leave permanent scars. Beyond physical symptoms, acne often affects confidence, emotional well-being, and quality of life.
For decades, Cutibacterium acnes—formerly known as Propionibacterium acnes—was widely regarded as the primary bacterial cause of acne. Yet researchers now recognize that the same bacterium is also naturally present on healthy skin. This finding has shifted scientific thinking from blaming a single microorganism to examining the broader ecosystem of microbes living on human skin.
According to Zahra and colleagues from Universitas Syiah Kuala, healthy skin contains a complex microbiome composed of bacteria, fungi, viruses, and other microorganisms that coexist in balance. Sebaceous areas such as the face, chest, and back are normally dominated by Cutibacterium acnes alongside beneficial microbes including Staphylococcus epidermidis. Rather than being harmful by default, these organisms help maintain skin acidity, strengthen the skin barrier, and prevent colonization by dangerous pathogens.
The review analyzed scientific literature indexed in PubMed and focused on studies published during the past five years. After screening titles, abstracts, and full texts, four major review studies were selected and categorized according to microbiome composition, bacterial strain differences, inflammatory pathways, and therapeutic implications.
The findings reveal that acne is closely linked to microbiome dysbiosis, a condition in which microbial balance becomes disrupted.
Instead of simply having more C. acnes, acne-prone skin tends to show:
- Reduced microbial diversity
- Dominance of more inflammatory C. acnes strains
- Altered balance between beneficial and harmful skin bacteria
- Stronger inflammatory activity within hair follicles
Healthy skin generally contains a wider variety of microbes and a more balanced distribution of C. acnes types. By contrast, acne lesions often show reduced microbial diversity and a predominance of aggressive bacterial variants.
The review identifies several acne-associated strains—particularly RT4, RT5, RT8, and RT10—as major contributors to inflammation. These strains differ significantly from variants more commonly found on healthy skin, such as RT6, which appears less inflammatory and more compatible with microbiome stability.
According to Zahra, these bacterial strains possess characteristics that make acne more difficult to control. They can form biofilms, protective layers that help bacteria survive inside follicles and resist treatment.
Biofilm formation creates several challenges:
- Stronger bacterial attachment to hair follicles
- Trapping of oil and keratin debris
- Increased follicle blockage and comedone formation
- Greater tolerance to antibiotics
- Longer-lasting inflammatory lesions
This mechanism helps explain why some acne cases persist despite standard therapy.
The review also describes acne as a multifactorial disease involving four interconnected biological processes:
- Increased sebum production
- Follicular hyperkeratinization or pore blockage
- Colonization by Cutibacterium acnes
- Activation of inflammatory pathways
Hormonal changes—particularly rising androgen levels during puberty—stimulate oil production and create a lipid-rich environment favorable for bacterial growth. Diet, stress, pollution, cosmetic products, and prolonged antibiotic use may further disturb microbiome balance and worsen inflammation.
One of the most important findings involves how inflammatory C. acnes strains activate the immune system.
These strains can stimulate receptors known as TLR-2 and TLR-4, triggering inflammatory pathways that increase cytokines such as:
- Interleukin-1β
- Interleukin-6
- Interleukin-8
- Tumor necrosis factor-alpha (TNF-α)
These inflammatory molecules attract immune cells and transform small clogged pores into visible acne lesions such as papules and pustules.
Zahra from Universitas Syiah Kuala notes that the inflammatory response appears influenced not only by bacterial quantity but also by microbiome imbalance and strain-specific virulence. Certain strains produce lipases, porphyrins, extracellular vesicles, and CAMP factors that intensify skin inflammation and tissue damage.
The findings carry important implications for acne treatment.
Conventional therapies—including antibiotics and benzoyl peroxide—primarily aim to reduce bacterial load and suppress inflammation. While often effective in the short term, these approaches may also disrupt healthy microbiome diversity and contribute to antibiotic resistance.
Because of this limitation, researchers are increasingly exploring microbiome-based therapies.
Emerging approaches include:
- Probiotics to restore microbial balance
- Bacteriophage therapy that selectively targets harmful bacterial strains
- Anti-biofilm agents to disrupt bacterial protection layers
- Precision treatment based on individual microbiome profiles
Rather than eliminating Cutibacterium acnes entirely, future therapies may seek to preserve beneficial strains while controlling aggressive variants associated with inflammation.
“Acne vulgaris is associated not only with the abundance of Cutibacterium acnes but also with skin microbiome dysbiosis and the predominance of more virulent strains,” Zahra concluded in the review.
The author also notes that current microbiome research still faces limitations. Most studies focus mainly on bacteria, while fungi and viruses on the skin remain less explored. Long-term studies are still needed to determine whether microbiome changes occur before acne develops or emerge as a consequence of inflammation.
These unanswered questions, however, are shaping a new direction in dermatology. The growing understanding of the skin microbiome suggests that acne management may soon move beyond simply killing bacteria toward restoring microbial balance and skin ecosystem health.
Author Profile
Putri Novian Zahra is a medical researcher from the Faculty of Medicine, Universitas Syiah Kuala, Aceh. Her academic work focuses on dermatology, inflammation, and microbiome-related mechanisms involved in skin diseases, particularly acne vulgaris.
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