Guide to Stability Testing of Cosmetics

Image used for illustrative purposes only

Manufacturers are advised to include routine stability testing into the lifecycle of their products. This critical data about the product helps them to not only create better products but also improve efficiencies in material management. Stability testing evaluates a product’s ability to maintain its original aesthetic, physical and chemical characteristics under controlled conditions designed to accelerate aging. Such testing can provide an early indication of problems that may occur in formulations.

Why is stability testing done?

Stability data is useful as an “early warning system” that alerts a formulator about problems related to formulation, Packaging etc. Such advance information can be helpful in many ways- Guide the chemist during product development; Ensure the product will continue to be aesthetically acceptable to the consumer; Determine the product will perform as intended and remain safe to use; Forewarn the manufacturer about problems which may occur after the consumer has purchased the product. Stability testing gives us an idea of the future risks and provides us guidelines to lay down a foundation for evaluation of future problems.

When is stability testing done?

  • Stability testing is done when a  new formulation is developed;
  • An existing on-market product has been reformulated
  • To qualify new raw material
  • The production method has been modified, or production has moved to a new facility or vendor
  • Changed packaging

How is Stability testing done?

A well designed stability testing protocol involves: 

  • Physical integrity which include Viscosity, Texture, Colour, Odour, Loss of Volatile constituents and Uptake of water.
  • Chemical Integrity which includes pH level , Degradation of active constituents , Interaction between constituents
  • Microbiological Stability
  • Packaging stability – Changes that occur in the container over a period of time including  leakage , corrosion and stress cracking

Accelerated stability testing

Accelerated stability testing is done to obtain stability data in short time. It involves exposure of the product to following parameters: Elevated temperature, Elevated humidity, Cycling tests, Freeze-thaw tests, Exposure to light and Mechanical tests

Elevated temperature: Storage at elevated temperature is vital, since the rate of chemical reaction roughly doubles for every ten degree increase in temperature. This test allows us to see certain problems much sooner than they would appear at room temperature. At each checkpoint the sample should be checked for following parameters – Physical attributes such as colour, odour, viscosity etc., Microbial Challenge test for preservative efficacy, Percentage of actives and Functional attributes.

Elevated Humidity: Since many products are adversely affected by moisture, storage at elevated humidity normally forms part of stability tests.

Freeze – thaw tests: Subjecting a product to alternate freezing and thawing can be of value in indicating the tendency of liquid products to cloud or crystallize or the physical stability of creams or other emulsions.

Cycling tests : Tests under conditions that are periodically changed can impose greater stress on samples than storage under constant conditions.Exposure to sunlight Where products are likely to be exposed to light in the market or in use, it is necessary to investigate the effect of such exposure. Mostly the effect of sunlight is seen as change in colour of the products.

Mechanical tests : Vibration test of samples can be useful in indicating whether demixing is likely to occur in powder or granular products; it can also serve as an indicator of  emulsion stability

Compatibility Testing 

Packaging Compatibility testing goes hand in hand with stability testing. This test highlights the interaction between contents & the immediate container. These interactions may be of following types

  • Sorption of constituents of the contents by the container.
  • Leaching of constituents of the container into the contents.
  • Adverse effects on the container such as corrosion.

Presently stability testing is obligatory for pharma across the world but not mandatory for cosmetics. Which means at some point of time , it may become mandatory for cosmetic manufacturers as well. In that case ,cosmetic manufacturers with routine stability testing processes in place would be in a better position.

Author : Mr Vinay Kumar Singh

Vice –President – R & D,

Ganesha Personal care Products

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