Stability testing for cosmetics helps ensure that a new or modified product’s functionality, aesthetics and quality are not adversely impacted during its intended shelf life and use.
There are no government standards for stability testing for cosmetics because of the wide variety of cosmetic products. A good manufacturer will have sound knowledge of industry guidelines and extensive formulating experience, allowing them to modify testing protocols and develop specific tests to assess a new or modified formulation.
What is stability testing?
Stability testing for cosmetics ensures product quality. Stability tests are predictive tests, aimed at assessing the ability of a product to maintain the desired physical, chemical and microbiological properties, as well as functional and aesthetic properties when stored and used under appropriate conditions by the consumer.
Stability tests also evaluate compatibility for market conditions in which the product is sold and used. Market conditions encompass distribution (transportation), storage and conditions during use.
There are three forms of stability tests:
- Physical and chemical integrity
- Microbiological stability
- Packaging stability
1. Physical/chemical stability test
Physical and chemical stability tests help the manufacturer predict how well cosmetic products react to common environmental stresses such as light and temperature extremes. Physical and chemical stability testing for cosmetics looks at the aesthetics (appearance, colour, odour, texture) as well as the stability of the formulation itself.
Common stability tests include:
- Cycle testing. This involves cycling the product through different temperatures. Each ‘cycle’ involves placing the product at -10°C for 24 hours, and then placing the product at 25°C (room temperature) for another 24 hours. If the product passes 3 cycles, it
- Temperature variations. Real-time stability testing for cosmetics is not always feasible, so high temperature testing is commonly used as a predictor of long-term stability. If a product is stored at 45°C for 3 months without issues, then it should be stable at room temperature for a period of one year.
- Centrifuge testing. When oil and water are mixed in an emulsion, there is a tendency for the product to separate. By placing the product in a rapidly rotating container to recreate extreme movement, manufacturers can see if separation will be a problem.
- Light exposure testing. Formulas and packaging can be sensitive to UV exposure and radiation. Manufacturers will expose products in transparent glass, the intended packaging and in an opaque container to compare how the formula and the intended packaging reacts to light exposure.
- Mechanical shock testing. Shipping movements may damage the cosmetic product or its packaging, so vibration testing (e.g.: on a pallet shaker) can reveal any issues.
2. Microbiological stability tests
Microbial contaminants usually come from two different stages: production and filling, and during consumer use. These contaminants affect the quality and longevity of the product.
Routine microbiological analysis of each batch of the finished product is essential to ensure the safety of the consumer and the quality of the product.
Microbiological stability tests for cosmetics include:
- Screening tests. Dip-slides or plate counts are used to determine whether a product is significantly contaminated.
- Quantitative tests. These tests determine the actual count level of bacteria, mold and yeast in a product.
3. Packaging stability tests
Stability testing includes packaging compatibility with the product. Packaging choices can affect the stability of the product because of interactions between the product, the package and the external environment.
Packaging may not fully protect the product or maintain the product’s aesthetic qualities (e.g. colour, fragrance). Product ingredients may also chemically react with the container.
Packaging stability tests for cosmetics include:
- Glass tests. Glass is the most inert material and does not react with a cosmetic product in any way, allowing the manufacturer to determine if the problem is the formula or the package.
- Weight loss tests. Weight loss evaluation helps to determine evaporation (water loss through the container’s walls or closure gaps such as lids).
- Leaking tests. The packaged product is tested in various orientations (upright, upside down, on its side, etc.) to determine any issues with leaks during transport and storage.
When should stability testing for cosmetics occur?
Stability testing is essential for new formulations and for ongoing quality control and quality assurance. Stability testing is also important for the following situations and conditions:
- New prototypes
- New raw material supplier
- New production site, equipment or procedures
- New or modified packaging
- Scaling up production
- New regulations
Image courtesy of Rutgers iJobs.