USP 51 Preservative Effectiveness Testing Method (and CTFA Method M-3)

Purpose of Test

Antimicrobial preservatives are substances typically added to non-sterile products (e.g. cleansers, cosmetics and other personal care products) to protect the product from microbiological growth. Effective preservation is important to ensure product quality and product safety and is commonly regulated by the U.S. FDA. The United States Pharmacopeia test and the Cosmetic, Toiletry and Fragrance Association (CTFA) Microbiology Guidelines method M-3 provide guidance on the assessment of preservative effectiveness.

Summary of Test

In these methods, a sample of the product is inoculated with a variety of bacteria, fungi and yeast organisms (typically Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus brasiliensis). The inoculated product is allowed to stand for up to 28 days and is periodically evaluated for surviving organisms. Depending on the type of product, specific reduction criteria may exist. Commonly, a 1.0-3.0 log10 reduction in organism is required after 14 days of exposure to the product with no increase in organism after 28 days.