The FDA requires that all cosmetics for consumer use be free of filth and void of any putrid or harmful substance that could be damaging to human health.
Bacteria are everywhere and can biodegrade (break down or feed on) most consumer products. Biodegradation can either cause the products to spoil or result in chemical changes that may be hazardous to the user. Microbiological contamination of cosmetics and personal care products during the manufacturing and production process is a common concern in the cosmetic industry.
An aerobic plate count for bacteria will indicate the level of bacteria in a product and can sometimes be used to indicate the quality and spoilage level of a product. Obtaining an estimate of the number of bacteria in a cosmetic product can assist in evaluating sanitary practices during manufacturing and processing as well as determining possible sources of contamination.
Bacterial plate counts are recommended to be performed on every batch of product following manufacture to ensure that the product is clean before being marketed to the public.
Bacterial counts are conducted by taking a sample of the product and placing it in a suitable neutralizer broth, and then plating dilutions to appropriate bacterial growth agar plates. Those plates are then incubated and analyzed to determine if aerobic bacteria are present in the sample, revealing the number of colony-forming units/g or ml. For talc and powder products, it is recommended for those to be tested for anaerobic bacteria in addition to aerobic bacteria. Anaerobic bacteria can survive in talc and powdered products for an extended period, so testing specifically for anaerobic bacteria can ensure that the product is not hiding any contamination.
If the product is contaminated upon evaluation, further evaluation the product using a test like the USP <62> – Test For Objectionable Microorganisms and possibly reformulation for better microbial protection may be necessary before being placed on the market for consumer use. If free of contaminants, then the product can continue on to be tested for preservative efficacy (challenge testing), safety, and stability prior to distribution.