As formulators build the latest creations, they must ensure that each part of the product meets its target and predetermined standards. Although characteristics such as aesthetics, fragrance, performance and color are market-dependent, preservative efficacy is not and must remain high. Preservatives are required to ensure that organisms do not grow and contaminate the product, and while it is necessary to ensure that all steps leading up to the development of the formula follow proper protocol—such as sanitary environment and microbe-free starting materials—a proper preservative system is crucial to ensure the long-term stability and safety of the product.
Across the industry, most companies have different methods and criteria to gauge their preservative system’s ability to inhibit microbe growth. Despite these variations, however, all formulators must ensure they develop a product that is not only effective at protecting against bacteria and fungi, but also is safe when applied to the skin. Irritation issues often arise from the improper use of preservatives, i.e. unnecessarily high levels of preservatives combined with materials that penetrate them deeper into the skin, which can lead to certain skin sensitization issues.1
Challenge testing: The test used to measure the efficacy of a preservative system is referred to as a challenge test. To perform this test, a product is inoculated with various organisms such as bacteria, yeast and fungi, then their rate of kill is measured during a defined length of time. Although challenge test protocols are slightly different throughout the personal care industry, they provide an effective benchmark of the strength of the preservative system.
There is no official preservative efficacy test for cosmetics, thus many larger companies have their own in-house challenge method and most of these methods have criteria that are much more stringent than either compendial or industry standards. Companies that do not have their own method may use the USP or Personal Care Products Council’s method as a way to determine preservative efficacy.2, 3