Preservative Challenge Screen

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Preservative challenge testing is a fast and easy way to learn about the efficacy of your preservative system.

Preservatives are ingredients used to protect a product from deterioration and help it perform as intended for the lifetime of the product. The efficacy of a preservative depends on the combination of the product’s ingredients and the packaging used. Therefore, preservative efficacy of a product cannot be predicted based on its individual ingredients alone. It must be established through microbial challenge testing of a complete formulation. The Preservative Challenge Test Screen is a pooled preservative challenge test for cosmetics that is recommended as an early indicator for preservative efficacy of cosmetics and personal care products. This is a test in which we purposely introduce specific microorganisms into the product, then watch the sample over a specified amount of time to see whether your preservative system is sufficient to eliminate those microorganisms.

The Preservative Challenge Screen utilizes 5 microorganisms, 3 bacteria and 2 fungi, specified in the USP <51> test method to challenge the products. However, this test is typically faster, more cost effective, and more challenging, making it a good indicator of efficacy for your preservation system. A preservative challenge screen for cosmetics consists of the 3 bacteria being pooled together and the 2 fungi being pooled together to be added to the product. One container of the product is challenged with the pooled bacteria and another with the pooled fungi. After the specified contact time, typically 7 days, the samples are analyzed to determine the level of bacteria and fungi remaining in the samples. If there are no microorganisms detected after the contact time, you can be fairly certain that your preservative system is working sufficiently. If the microorganisms are detected in the sample, don’t fret, there is still hope as long as there are less remaining than we started with. However, if there are more or the same level of microorganisms remaining as when we started, then you should begin looking into ways to improve your preservation system.

Why Use Preservatives?

Consumer products are expected by the FDA to withstand microbial attack within the intended period of use of the product. Without preservatives, cosmetics and personal care products are likely to become contaminated with various microorganisms, leading to product spoilage and possibly irritation or infections caused by harmful microorganisms.

From the time a cosmetic or personal care product is opened to the time it is discarded, it is subject to constant microbial contamination from the environment and the consumers’ hands and body. For example, touching an applicator to your face which has low levels of microorganisms on it and then placing the applicator back in the product is a common source of potential contamination. Temperatures and humidity levels in home environments where cosmetic and personal care products are typically located, such as in warm, moist bathrooms are perfect for enhancing microbial growth in a product unless it is well preserved. Now, that same microorganism that has just been introduced to the product by the applicator has been allowed to grow in the product in the bathroom. Therefore, the next use will be a self-inoculation with higher levels of the microorganism, which can cause various unpleasant problems for consumers, including skin and eye area infections. Preservatives are used to help prevent these product contamination problems.