Selection of wet wipes for preservation - Comparison of preservative efficacy evaluation methods for wet wipes products (USP<51> & PCPC M-5)

Due to their portability and ease of use, wet wipes have become an indispensable disposable hygiene product in the daily lives of more and more consumers. However, what many people do not know is that compared with other personal care products, wet wipes are more susceptible to microbial contamination.

The reason is that although the basic composition of wet wipes is only a combination of non-woven fabrics and a certain amount of wet wipes liquid (i.e., functional liquid), and the liquid formula is mainly water and a small amount of nutrients, this high-moisture, trace-nutrient-rich environment is very easy to breed bacteria and molds - whether in production, storage or consumer use.

Therefore, in order to ensure the microbiological quality and safety of wet wipes products, manufacturers need to pay special attention to the selection of preservative systems and the determination of the amount of preservatives added during the formulation design stage. The effectiveness of the preservative system is usually evaluated by the internationally recognized preservative efficacy evaluation test (PET), also known as the preservative challenge test.

At present, domestic wet wipes products mainly refer to the following two methods when conducting antiseptic performance tests:

1. United States Pharmacopoeia USP<51>: Antimicrobial Effectiveness Testing

This method uses **extruded liquid (i.e. wet wipes liquid)** in finished wet wipes as the test sample for challenge test. The advantages are simple operation, good repeatability, and high detection efficiency. It is suitable for wet wipes products with low adsorption of non-woven fabrics to antiseptic active ingredients. Since most of the antiseptic active ingredients are retained in the extruded liquid, the test results can better reflect the actual antiseptic ability of the entire wet wipes product.

2. PCPC (formerly CTFA) M-5: Special antiseptic test method for non-woven materials

This method was developed by the Personal Care Products Committee of the United States. In the test, the microbial liquid is directly inoculated into the four corners and center of the wet wipes sample (five-point method) to observe the growth of microorganisms on the non-woven fabric matrix. Since this method directly evaluates the actual performance of the antiseptic system in the wet wipes carrier, it is closer to the actual use environment of the product.

However, compared with USP<51>, the M-5 method is more complicated to operate and has a longer experimental cycle, so its promotion in actual testing is relatively limited. However, for wet wipes products whose nonwovens have strong adsorption to preservatives, if only the extruded liquid is tested, the antiseptic effect may be underestimated. At this time, the M-5 method can more comprehensively evaluate the antiseptic performance of the product.

3. Which method is more suitable for wet wipes antiseptic performance testing?

In fact, the two methods have their own focuses:

If the preservative in the wet wipes liquid in the wet wipes product is not easily adsorbed by the carrier, the USP<51> is more convenient and efficient, and is suitable for daily rapid screening;

If there is a strong adsorption effect between the preservative and the nonwoven, it may lead to a low concentration of the active ingredient in the extruded liquid. At this time, the M-5 method can more truly reflect the actual effectiveness of the antiseptic system in the final product.

Conclusion

In summary, both USP<51> and PCPC M-5 are currently widely recognized and recommended wet wipes liquid antiseptic performance evaluation methods. Each manufacturer and third-party laboratory can choose the most appropriate testing method based on the specific formula characteristics and usage scenarios of the wet wipes products to ensure the microbial safety and stability of the products throughout their life cycle.