Unlocking the Secrets of a Fermented Milk Postbiotic: How it Balances Skin Microbes and Fights Off Pathogens — But here's where it gets controversial... Recent research from Jiangnan University in China, in collaboration with Hangzhou Island Xingqing Biotechnology, reveals fascinating insights into how a specially prepared fermented milk ingredient influences skin bacteria. This study suggests that instead of broadly killing bacteria—a common approach in many skincare products—this postbiotic encourages the growth of beneficial microbes while suppressing harmful ones. This could revolutionize how we think about maintaining skin health and microbiome harmony.
Here's the full story: the researchers developed a unique fermented milk product, derived from milk that had been de-lactosed (meaning the sugar lactose was removed), broken down with enzymes, and then fermented using Lactobacillus plantarum (a friendly probiotic bacteria). After fermentation, the mixture was filtered and freeze-dried. Importantly, this product contains metabolites and peptides produced during fermentation but does not contain live bacteria. Think of it as a concentrated, bioactive essence that can influence bacterial behavior on your skin.
From Killing to Rebalancing: Traditional antimicrobial ingredients—such as preservatives—often wipe out all bacteria indiscriminately. While this might seem effective, it can disrupt the natural balance of our skin microbiome, disturbing the friendly bacteria that protect and maintain healthy skin. This disruption can impair the skin's barrier function and may even lead to more problems down the line.
Instead, this study explored a more nuanced approach. Instead of eradicating all bacteria, they aimed to shift the microbial balance towards beneficial bacteria—those that support healthy skin. They focused on three key bacteria:
- Staphylococcus epidermidis — a ‘friendly’ bacterium that naturally resides on healthy skin,
- Staphylococcus aureus — a well-known pathogen linked to skin conditions such as eczema and infections,
- Escherichia coli (E. coli) — a reference strain used to evaluate antimicrobial properties.
The scientists prepared two different milk-based formulations: one was an enzymatic hydrolysate of skim milk (used as a control), and the other was this same hydrolysate fermented with L. plantarum. When tested separately, the control milk (PM) encouraged growth across all three bacteria, which isn’t surprising given that nutrients generally support bacterial growth.
In stark contrast, the fermented milk (FM) showed a selective effect. It notably boosted the growth of S. epidermidis but significantly suppressed the viability of E. coli and S. aureus at a concentration of 100 mg/mL over 24 hours. This remarkable differentiation hints strongly at the importance of fermentation and the metabolites it produces, which appear to help favor the good bacteria while weakening the bad.
Realistic Simulation of Skin Microbiota Interactions: To make the experiment closer to real-life skin conditions, the team used co-culture models—meaning they grew helpful and harmful bacteria together to see how they would compete. In one setup, S. epidermidis was pitted against E. coli. Usually, E. coli dominates, but when fermented milk was added, the balance tipped—S. epidermidis flourished while E. coli was kept in check. This was especially clear within the first half-day, demonstrating the product’s ability to promote beneficial bacteria precisely when they are most needed.
In another model, S. epidermidis was grown alongside S. aureus. Using a special chamber separated by a membrane that allows only chemicals to pass, researchers observed that in control conditions, both bacteria thrived. However, with fermented milk, S. aureus was strongly suppressed, and S. epidermidis remained relatively unaffected over 24 hours. Although S. aureus showed some signs of recovery later, the trend was clear: the fermented milk slides the balance in favor of helpful microbes, diminishing the threat of pathogenic bacteria.
Deciphering the Mechanism: Acid Stress and Energy Drain: How does this fermented milk product selectively inhibit pathogens? The team took a deeper dive into the metabolic changes induced by the treatment. They analyzed the small molecules—the metabolites—produced during fermentation. This comprehensive profiling revealed thousands of shifts in bacterial metabolism, with a key molecule coming into focus: pyruvate, a central compound in energy production.
FM treatment increased the conversion of sugars and amino acids into pyruvate, which led to sharply increased levels of organic acids like lactic and propionic acids. These acids can penetrate bacterial cell walls, lowering internal pH and creating a stressful environment for bacteria, especially pathogenic ones. To survive, harmful bacteria must expend vast amounts of energy pumping out acids and repairing damage—slowing their growth severely.
Interestingly, S. epidermidis appears better equipped to manage these acidic conditions, utilizing buffering pathways and tolerating the environment much more effectively. This environment effectively starves pathogens, giving beneficial bacteria a chance to thrive while suppressing harmful microbes.
A Promising Strategy, But Not Without Limitations: The researchers acknowledge that their study is initial and conducted under controlled laboratory conditions—using only a handful of bacterial strains at a consistent temperature and pH. The real skin is far more complex, hosting a diverse microbiome that varies by location and environmental factors. So, while these results are promising, they can’t yet be directly applied to human skin without further research.
That said, this study offers compelling evidence that manipulating bacterial metabolism—not just killing bacteria—can provide a more gentle and precise way to support skin health. Such fermentation-based postbiotics could become key ingredients in future skincare formulations, offering a microbiome-friendly alternative to harsh preservatives and antimicrobial agents.
In the ongoing conversation about skin microbiome health, could targeted metabolic modulation be the game-changer we’ve been waiting for? Or will there be unforeseen challenges as we move toward more nuanced microbiome management? Share your thoughts—do you see this as the future of skincare or a temporary trend?
