Parameters for Stability Studies on Cosmetics

Cosmetic products have been in use since time immemorial but in the recent past there has been an upsurge in demand for personal healthcare and beauty products due to increased awareness. USA and European Union were traditionally the leading markets but other developing economies have also contributed to market growth of such products. Regulatory bodies around the globe have come up with stringent requirements to ensure safe use of cosmetics and such requirements also includes stability studies which guarantee that products retain their proclaimed features over their shelf life.

Stability Test Parameters

The stability studies on cosmetic products are designed to ensure that the product or modified versions meet the intended physical, chemical and microbiological quality standards as well as functionality and aesthetics when stored under prescribed conditions. Such tests broadly speaking fall under three classes:

Physical : chemical: appearance, colour, odour/fragrance, viscosity, texture, flow and emulsion stability, density, refractive index, light stability, etc. Accelerated stability testing is used to arrive at the expiry date of the product.

Microbiological : contamination with growth of bacteria, mould and yeast.

Packaging Compatibility: integrity of the package and the product under the expected conditions of storage and transportation.

Cosmetic and personal healthcare products fall in several usage categories and sub-categories.It is not possible to elaborate upon details of stability testing on all the categories and in this brief article an attempt is made to outline some of the general test parameters.

Physical/Chemical Tests

• Light exposure often leads to discolouration of the product or the package/label.
• Centrifuge test is used to test stability of emulsions. Separation of emulsion layer or of oil droplets is referred to as creaming. The emulsion is heated to 50°C and centrifuged for 30 min at 3000 rpm.
• Temperature cycling at elevated temperature provides accelerated stability testing. Some tests are conducted at 45°C or 37°C for three months. Routine room temperature studies (25°C) are required to be conducted for two years. Freeze – thaw cycling reveals detail on product stability. It is done at 0°C or -10°C. Product is kept at -10°C for 24 hours and at 25°C for next 24 hours (referred to as cycle). A product passing these cycles tests is considered stable. If the temperature is cycled between -10°C and 45°C for three 24 hour cycles it is considered to be a high-quality product.
• Mechanical shock testing is done to determine if shipping movements can damage the product or its packaging. At different stages of such tests measurements can be made for colour, fragrance, viscosity, pH value, particle size, etc..

Packaging

Packaging prevents the product interaction with the environment. It protects the product from oxidation by air or exposure to water vapour. At the same time it prevents loss of fragrance by evaporation of volatile components. Tests on packaging include leakage tests, weight loss tests and testing in inert containers.

Microbiological Stability Tests

Microbiological contamination can result during manufacture, transportation or during usage by consumer. It can result in deterioration of quality of the product. Screening tests using rapid semi qualitative or quantitative tests involving enrichment culturing and colony counting are often employed.

In a subsequent article stability chambers will be covered which are used for conducting stability studies on a range of products covering pharmaceuticals, foods and cosmetics.

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