Inside Cosmetic Microbiology - What Every Brand Needs to Know Before Launch

Before we dive into our upcoming webinar on Cosmetic Microbiology, Stability & Quality Testing, we wanted to give you a behind-the-scenes look at the science that quietly protects every great product. We’re joined by Dr. Marisa Isaacs, Director of Operations at Stratum Analytical, a Canadian laboratory specializing in microbiological, molecular, and chemical testing for the cosmetic industry. With over a decade of experience across microbiology, chemistry, and regulatory strategy, she works closely with beauty brands to ensure product safety, quality, and compliance at every stage of development. 
Let’s be honest—microbiology and stability testing aren’t the most glamorous parts of beauty… but they are absolutely the reason your product works safely, consistently, and over time. From shelf life to preservation, this is where science meets trust. To make things more real (and a lot more interesting), we sat down with Dr. Isaacs to break down what actually happens in the lab, what brands often get wrong, and what really matters before going to market.
1. For brands that are just starting out, microbiology and stability testing can feel overwhelming. What are the absolute must-have tests every product should go through before going to market?

​The key is to focus on tests that ensure safety, shelf life, and regulatory compliance, without overcomplicating things. While requirements vary by region, there is strong global overlap. Below is a practical, region-specific breakdown of “must-have” microbiology and stability testing before going to market.

​2. Can you walk us through what actually happens in a lab during microbiological and stability testing? What would surprise most beauty brands?

When people think of microbiological and stability testing, they often imagine a quick check to confirm a product is “safe.” In reality, what happens in the lab is much more rigorous. For example, in preservative challenge testing, we deliberately contaminate the product with known microorganisms such as bacteria, yeast, and mold, and then monitor it over 28 days. The goal is to determine whether the preservative system can effectively control and reduce contamination over time. It’s less about whether the product is clean on day one, and more about whether it can defend itself throughout its lifecycle and during real-world use.

A common surprise is the level of rigor behind the data itself. Results don’t simply come off an instrument and get reported—they go through multiple layers of independent review, typically an internal verification followed by a third review from an independent quality assurance associate. This ensures that what’s reported is accurate, reproducible, and defensible. Finally, many brands are surprised by how dynamic products can be. A formulation that looks perfect at launch can evolve over time, and small decisions in formulation or packaging can significantly impact stability and preservation. These tests are designed to challenge the product under worst-case conditions, because that’s ultimately what protects the end user.

3. A lot of brands try to minimize costs early on. Where do you see companies making risky compromises when it comes to quality and safety testing?

Many companies perform microbiological testing when the product is fresh off the production line. While this can confirm that the product starts within acceptable limits, it can create a false sense of security. There is often an assumption that microbiological quality, and the effectiveness of the preservative system, will be maintained throughout the product’s entire shelf life—but this is not always the case. As a product ages, microbial burden can increase, and preservative systems can weaken or break down. This may result in the product failing microbial limits or becoming insufficiently preserved toward the end of its life, posing a potential safety risk to consumers. Best practice is to conduct both initial and real-time, end-of-shelf-life  microbiological testing to ensure quality and safety across the entire lifecycle of the product. Issues related to deteriorating preservative systems can be missed in accelerated testing alone.

4. Testing reports can be quite technical. What are the key things founders or brand owners should actually be looking for when reviewing their results?

Testing reports can definitely feel overwhelming, but founders don’t need to interpret every detail. The key is knowing what to focus on and what signals potential risk. First, look at the pass/fail status—but don’t stop there. A “pass” doesn’t always mean everything is perfect; it simply means the product met the minimum criteria at that specific timepoint.

For microbiology, pay close attention to:

• Microbial limits results (are counts well below limits or borderline?)

For stability, focus on:

• Trends over time, not just individual data points
• A major red flag is when results are trending in the wrong direction, even if they are still technically passing.
• Also, look for consistency across batches. If one batch passes easily and another is borderline, this may indicate a manufacturing or formulation issue.

It is also important to ensure the laboratory itself is reputable. A high-quality lab report clearly identifies the sample, methods used, and results with appropriate units and acceptance criteria. It should also include key testing conditions (such as timepoints and storage parameters), along with documented review and quality assurance sign-off. Overall, the report should be transparent, traceable, and defensible.

5. Are there any new or emerging testing methods—like microbiome testing or in vitro approaches—that brands should start paying attention to?

Emerging methods such as microbiome profiling, advanced in vitro models, and predictive stability tools are gaining attention, but they should be approached with caution in a regulatory context. Many of these approaches are still evolving in terms of standardization, validation, and regulatory acceptance. While they can provide valuable R&D insights or support marketing narratives, they are not yet recognized as substitutes for established safety and quality testing. For example, microbiome testing does not assess contamination or preservative effectiveness—it simply characterizes microbial populations, which are highly variable and influenced by environmental factors. This variability makes the data difficult to interpret and not directly actionable from a safety perspective.
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As a result, the foundation of cosmetic testing should remain compendial, validated methods, such as USP and ISO standards, performed in accredited laboratories. These approaches are widely accepted by regulators and provide a clear, defensible basis for demonstrating product safety and stability. Emerging tools are worth monitoring, but for now, they should be viewed as complementary rather than essential.

6. From your experience, what are the most common mistakes beauty brands make when it comes to stability or microbiology, and how can they avoid them?

One of the biggest mistakes I see is brands designing products for ideal conditions rather than real-world use. A formula may pass stability and microbiological testing in a controlled lab setting, but struggle once it’s exposed to repeated opening, temperature fluctuations, or day-to-day consumer handling. Testing doesn’t always reflect how the product actually performs in the market. The shift toward “clean” formulations often involves reducing or eliminating preservatives, but the associated microbiological risks aren’t always fully accounted for. Preservatives are a primary defense against contamination, and when they are removed, the product inherently becomes more vulnerable. Without a corresponding increase in testing rigor or alternative risk mitigation strategies, this can create gaps in product safety and performance.

I also frequently see formulation and packaging decisions made in isolation, when they should be treated as a single system. The same formula can behave very differently in a jar versus an airless pump, yet packaging compatibility and in-use contamination risk are often under-evaluated. Stability studies should be conducted in the final container and repeated if there are changes to the packaging design. A less obvious gap is the lack of ongoing surveillance testing once a product is commercialized. Many brands generate strong initial data but do not continue to monitor product performance across manufactured batches. In reality, variability can be introduced through changes such as new raw material suppliers, manufacturing scale-up, or subtle process shifts. Incorporating periodic checks—such as potency or preservative efficacy testing every 6–12 months, or when key inputs change—can help identify drift before it becomes a quality or safety issue.

Stratum Analytical Website