Let's talk about something most people in this industry aren't talking about yet.
When someone comes to you with thinning hair, the conversation usually starts and ends with hormones. DHT. Genetics. Maybe stress. And yes, those things matter. But a study published in mSystems (American Society for Microbiology) in 2025 just added an entirely new layer to the conversation. One that changes how we think about assessment, treatment, and even early detection.
The study looked at the scalp microbiome, the entire ecosystem of bacteria and fungi living on your scalp, and found that people with androgenetic alopecia have measurably different microbial communities than people without it. And the more severe the hair loss, the more disrupted the microbiome.
This isn't a blog post from a supplement company. This is peer-reviewed, multi-kingdom sequencing data. Let me break it down.
What They Did
Researchers collected scalp microbiome samples from patients at varying stages of androgenetic alopecia and compared them to healthy controls. But here's what made this study different from the handful of microbiome studies that came before it: they used 16S rRNA and ITS1 sequencing, meaning they mapped both the bacterial and fungal communities simultaneously. Most previous studies only looked at one or the other.
Then they ran the data through machine learning models to see whether the microbial patterns could actually predict hair loss severity. Spoiler: they could.
What They Found
The findings are significant. Let me walk you through the key ones.
The Bacterial Side
Propionibacterium, a bacteria you might recognize from acne research, was significantly enriched in people with androgenetic alopecia. The researchers believe this is driven by sebaceous gland hyperplasia (overactive oil glands), which creates an environment where this particular bacteria thrives. The problem? Its overgrowth triggers inflammatory responses in the follicle, contributing directly to miniaturization.
On the flip side, Corynebacterium, generally considered a commensal (beneficial or neutral) resident of healthy skin, decreased as hair loss got worse. Think of it like your scalp losing its "good bacteria" while the inflammatory ones take over.
The Fungal Side
Here's where it gets really interesting. Malassezia, the fungus most of us associate with dandruff and seborrheic dermatitis, actually declined as hair loss severity increased. That's counterintuitive to what a lot of professionals assume. Meanwhile, Alternaria, a fungal genus that stayed low in healthy individuals, surged past 50% relative abundance in the most severe AGA cases.
That's a massive shift in the fungal ecosystem. And it tells us something important: the scalp environment in advanced hair loss is fundamentally different from what most people think it is.
The Whole-Scalp Problem
One of the most clinically relevant findings: the dysbiosis wasn't just happening where the hair was thinning. It was present across the entire scalp. That means the microbial disruption in someone with AGA is systemic to the scalp, not localized to the areas of visible loss.
If the microbial imbalance extends beyond the areas of visible thinning, it means we need to be treating the entire scalp environment, not just targeting the spots where loss is most obvious. Your scope assessment, your treatment protocols, your topical recommendations, all of it should account for this.
The study also found that in healthy subjects, the scalp microbiome changes predictably with age. But in AGA patients, that age-related pattern was completely disrupted. The microbiome looked chaotic, out of step with what their age would predict.
MiSCH: A Scalp Health Score
Perhaps the most forward-looking part of this research: the team created something called the Microbial Index of Scalp Health (MiSCH). It's a quantitative score from 0 to 100 that measures how healthy, or how disrupted, your scalp microbiome is.
Higher scores indicate a healthier microbiome. Lower scores correlate with more severe AGA. And here's the breakthrough: MiSCH was able to identify high-risk individuals who had severely disrupted microbiomes but no visible hair loss yet.
Read that again. They could detect the problem before the hair started falling out.
That's early detection. That's personalized treatment. That's the future of what we do.
What This Means for You
If you're a trichology professional, or becoming one, this study should shift how you think about three things:
1. Assessment goes beyond the scope. Yes, trichoscopy is essential. But the scalp environment is more complex than what we can see at 50x magnification. Understanding that microbial imbalance plays a role means asking better intake questions about product use, scalp conditions, inflammatory markers, and lifestyle factors that affect microbiome health.
2. Treatment is about the environment, not just the follicle. If you're only targeting DHT or only stimulating growth, you're missing half the picture. The scalp is an ecosystem. Treatments that support a healthy microbial balance, alongside growth stimulation, are going to produce better outcomes.
3. Prevention is becoming real. MiSCH is still in research phase. But the direction is clear: we're moving toward being able to identify people at risk for hair loss before it starts. That changes the entire client conversation from "let's try to fix this" to "let's prevent this from happening."
The Bottom Line
Hair loss isn't just hormonal. The 2025 multi-kingdom sequencing study confirms that scalp microbiome dysbiosis, bacterial and fungal, is a measurable, predictable component of androgenetic alopecia. And the disruption happens across the entire scalp, not just where you see thinning. The practitioners who understand this, and build it into their assessment and treatment approach, are the ones who will deliver the best outcomes for their clients.
The Study
If you want to read the full paper yourself (and I always encourage it), you can access it here: