Stability Testing in Cosmetics: Crucial to Consumer Experience
It is probably a question that rarely the consumer's mind. Is this tube of cream still as effective as it was when I opened it?
Experienced cosmetic chemists commonly cite a persistent problem in formulation: initial test success does not guarantee long-term stability, as products can exhibit instability, such as separation, discoloration, or microbial proliferation, sometimes in as little as three months. Stability testing is critical to ensuring product quality and self-life in the product development lifecycle.
Why Stability Testing Matters
Let's face it, stability testing is not the most captivating part of the process when it comes to cosmetic formulation. The work that goes into creating a formula from ingredients that bring meaningful results to the customer is almost always the primary focus. It is essential to apply the same degree of focus and consideration to the ingredients that are not prominently displayed on the front label.
The lesser-known components of the formula play a crucial role in ensuring the product remains stable, fresh, and ready for customer use. It is arguably the foundational element of a product, a critical component ensuring efficacy, stability, and safety. According to recent industry guidelines, proper stability testing isn't just about making sure your product doesn't separate—it's about ensuring every aspect of your formula maintains its integrity over time[1]. It is this ability for your product to deliver weeks or months after the purchase that cements your brand perception in the customer's mind.
Types of Testing
Different products require different types of testing based on their intended purposes, application, and target market. Testing can be customized to ensure proper development by providing specific data.
Formula Stability Testing
This is a fundamental test that ensures the mix of ingredients chosen to deliver specific results work together and for the life of the product. It is the foundation of product development and it should never be overlooked during the development process. While the FDA doesn't mandate specific stability tests for cosmetics, they do require all products to be safe for consumer use.[2] In some cases, as with Over the Counter (OTC) products, the FDA recommends including a minimum of three points of time in accelerated stability studies: zero, three, and six months.3
Two techniques are available for performing stability testing, each presenting its own set of advantages and disadvantages. Nevertheless, the objective is to generate outcomes from both that yield results within a close range of each other. The two techniques are Real-Time and Accelerated testing.
Real-time stability testing demonstrates the product's performance in typical storage conditions as time progresses. This process is considered the gold standard; however, its completion time is equivalent to the desired shelf life. Waiting for results from this type of testing prior to product launch may not be feasible for most consumer products, which is the reason for Accelerated Testing procedure.
The standard accelerated test in the industry commonly requires subjecting products to increased temperatures between 37°C (98F) and 45°C (113F) at specific intervals.[4] This testing method may also involve subjecting the formula to freezing temperatures. The product's journey from production to the consumer may involve trucking through freezing winter conditions, impacting the product's formula. Consumer products typically undergo multimodal transport across land, sea, and air en route to retail outlets, requiring their formula to withstand a wide range of temperatures. However, the inherent imperfections of accelerated testing warrant acknowledgment, a point often missed. Products successfully completing accelerated testing may nonetheless fail under real-world conditions, and conversely.
Compatibility Testing
To reach the consumer, a formula must be packaged. Compatibility testing encompasses three main types: chemical compatibility, physical compatibility, and biological compatibility.[5] As packaging can vary widely across the market, it is important to ensure the formula remains stable while in its container. The compatibility of the product with its packaging is determined by conducting stability tests in both inert packaging (e.g., glass containers) and in the final packaging.[6]
Light and Exposure Testing
This series of testing is particularly important for clear and transparent packaging. The formula's ingredients’ susceptibility to UV light should be considered. Just as sunlight bleaches a poster, some ingredients degrade when exposed to UV rays. Products on display shelves or counters, particularly those in direct sunlight all day, are especially susceptible. The formula's stability in clear packaging is crucial to prevent light-induced degradation, which could lead to loss of efficacy, spoilage or even safety hazards.
Preservative Efficacy Testing (PET)
According to ISO 11930 standards, PET is a reference method to evaluate the preservation of cosmetic formulations.[7] This testing evaluates the ability of preservatives to prevent the growth of microorganisms, including bacteria, yeast, and mold.[8] There are two main categories that preservatives fall into, although there are others as technology advances, natural and synthetic.
For both types, this testing stresses the formulas by introducing quantities of test organisms into the formula and monitoring their survival over time. These trials generally extend for a period of 28 days, with measurements taken at predetermined intervals to assess the efficacy of the preservatives in inhibiting or eliminating bacterial growth; results are reported as pass or fail. Multiple standards exist for this test; confirm your lab and manufacturer comply with at least one.
The Hidden Challenges in Stability Testing and Why We Do It
Bridging the gap between the lab and the customer's bathroom shelf is imperative for the success of your product and ultimately your brand. The development of an innovative formula is just one part of the process. The development and market introduction of products that address consumer needs is a worthy pursuit. However, should your product fail to meet expectations, the considerable effort invested in market penetration will have been wasted. There are thousands of great products out there and the customer has so many choices. Truly delivering a good product is becoming more challenging as customer expectations rise with the myriad of choice. Invest in your formula with proper testing to ensure efficacy months beyond the sale will separate your brand from the rest.
The Future of Stability Testing
The cosmetics industry is evolving, and so are testing methods. New guidelines introduced in 2024 required more stringent requirements for stability testing, particularly for natural and clean beauty products.[9] Protect your brand perception and customer trust by working with your supplier to understand the latest testing protocols available.
Final Thoughts
Remember, stability testing isn't just a regulatory requirement—it's your product's insurance policy. A well-designed stability program might seem expensive and time-consuming, but it's far less costly than a market recall or damage to your brand's reputation.
Your stability testing program should be as unique as your formulations. While following industry standards is crucial, understanding the specific stress factors your product might face in the real world is equally important. After all, the goal isn't just to pass testing—it's to create products that consistently meet your customer's expectations from first use to the last.
Sources:
[1] Kirkbride, L., et al. (2021). Designing a suitable stability protocol in the face of a changing retail landscape. Cosmetics, 8(3), 64.
[2] FDA. (2022). Modernization of Cosmetics Regulation Act of 2022 (MoCRA). U.S. Food and Drug Administration.
[3] Certified Laboratories. (2023). Accelerated Stability Testing for Cosmetics & OTC Products.
[4] Postles, A. (2019). Factors affecting the measurement of stability and safety of cosmetic products. Bournemouth University.
[5] Cosmopacks. (2024). The Importance of Package Compatibility Testing for Cosmetic Packaging.
[6] Cosmetic Testing Lab. (2024). Stability and Compatibility Test Guidelines.
[7] ISO 11930. (2023). Cosmetics — Microbiology — Evaluation of the antimicrobial protection of a cosmetic product.
[8] ChemLeg. (2024). Protective Efficacy Testing in Cosmetics.
[9] CISEMA. (2024). Cosmetic Packaging Compatibility Testing Guidelines.