The purpose of stability testing cosmetic products is to ensure that a new or modified product meets the intended physical, chemical and microbiological quality standards as well as functionality and aesthetics when stored under appropriate conditions. Because the development cycle of cosmetic products is relatively short, and also, in order that the testing activity does not become economically disproportionate in view of the multitude of product launches each year, each manufacturer must have at their disposal tests that are adapted to their activity. Each manufacturer should design their stability testing program such that it is reasonable and efficiently addresses the testing required. (Guidelines on stability testing of cosmetic products - Colipa)
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The specific tests performed during stability testing will vary depending on the type of cosmetic product, but they typically include:

- Physical tests: These tests measure the appearance, texture, and color of the product.
- Chemical tests: These tests measure the concentration of ingredients in the product and the presence of any harmful substances.
- Microbiological tests: These tests measure the number of bacteria and other microorganisms in the product.
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Stability testing is typically conducted over a period of several months or even years, and the product is tested under a variety of conditions, such as different temperatures, light levels, and humidity levels. The results of stability testing are used to determine the shelf life of the product, which is the length of time the product can be stored and still meet its intended quality standards.

Stability testing is an important part of the development and marketing of cosmetic products. It helps to ensure that consumers are using safe and effective products that will not deteriorate over time.

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