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Stability testing in cosmetic products is a fundamental evaluation process that ensures a product remains safe and effective throughout its shelf life by determining whether its physical, chemical, microbiological, and sensory properties are preserved over time.
The quality of a cosmetic product is not solely defined by its formulation ingredients. Its long-term safety, effectiveness, and physical integrity are also closely linked to the packaging. In this context, stability tests are critical analyses that assess whether a product can maintain these properties throughout its shelf life. But why is conducting these tests in the original packaging so crucial?
Purpose of Stability Testing
Stability analyses reveal whether a cosmetic product undergoes any changes over time in terms of:
Physical attributes like color, odor, and texture
Physicochemical parameters such as pH, viscosity, and density
Effectiveness of active ingredients
Microbiological stability
These analyses help determine whether the product is safe for use for the entire declared shelf life.
Original Packaging Simulates Real Usage Conditions
From manufacturing to consumer use, cosmetic products are exposed to numerous external factors—heat, light, humidity, mechanical stress, etc. Stability tests are designed to simulate these conditions. However, conducting tests in the original packaging is necessary due to the following reasons:
✔ Packaging permeability: Light or oxygen permeability can impact the product's oxidative stability
✔ Cap structure and sealing: Determines how well the product is protected from external influences
✔ Material durability: Resistance of the packaging to stress factors such as heat and pressure directly affects the test outcomes
Taking all these factors into account, using the original packaging simulates the product’s actual lifecycle before reaching the consumer.
Packaging-Material Interactions Are Evaluated
Some formulation ingredients may react with the packaging material over time. Especially:
Volatile components (e.g., essential oils) may evaporate or migrate through the packaging
Pigments may undergo color reactions with the packaging
pH-sensitive actives may degrade due to interactions with the packaging material
Such interactions can negatively impact the product’s effectiveness, safety, and aesthetic appearance. Stability tests also objectively assess the influence of packaging on the product.
Shelf life determination in cosmetics should not be based on the formulation alone. True shelf life should consider the compatibility between the formulation and its packaging.
► A product’s ability to remain stable under storage conditions over time depends not only on ingredient stability but also on the protective capacity of its packaging.
Can Alternative Packaging Be Used?
In certain cases, the original packaging may not be available yet, or the testing and production processes may progress in parallel. In such cases, alternative packaging can be used if the following criteria are met:
Material type: The alternative must match the original (e.g., HDPE, PET, glass, etc.)
Permeability and thickness: Must be equivalent in terms of oxygen, UV, and moisture transmission
Sealing properties: Cap design and sealing features (e.g., tamper bands) must be identical
Only under these conditions can the validity of the test be ensured.
What Do the Regulations Say?
ISO/TR 18811:2018 serves as an important reference for stability testing and packaging interaction evaluation. Similarly, the EU Cosmetics Regulation (EC No 1223/2009) recommends assessing stability data together with the packaging in the product safety dossier. In line with these regulations, at COSMING Laboratory, we perform all stability tests using either the original or equivalent packaging materials.
Don't Overlook Packaging—Test It Right
No matter how high-quality your cosmetic formulation is, without the support of suitable packaging, it may not maintain its real performance. Conducting stability tests with the original packaging is not just a procedure—it is a cornerstone of product safety and consumer satisfaction.
For support in stability analyses and cosmetic regulatory consultancy, feel free to contact our expert team at COSMING.
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