Yeast and molds are types of fungal cells that can cause various degrees of deterioration and decomposition of cosmetics and personal care products.
Since yeast and molds are ubiquitous (occurring everywhere) in nature, cosmetics and personal care products are just as susceptible to fungal contamination as they are to bacterial contamination.
Cosmetic products are susceptible to attack from yeast and molds due, in large part, to their relatively versatile environmental requirements. The pH range required for growth for mold and yeast is quite broad, spanning a pH of 2 to greater than a pH of 9. Their growth temperature range is also quite broad, typically falling between 10°C and 35°C, with a few species capable of growth above and below this range.
An aerobic plate count for yeast and mold is a simple screen to tell you whether your product is contaminated with fungi. Total Yeast and Mold Counts go hand-in-hand with Aerobic Plate Counts for Bacteria and are recommended to be performed on every batch of product to be sold to ensure that the product is safe for consumer use.
A Total Yeast and Mold Count is conducted by taking a sample of the product and placing it in a suitable neutralizer broth and plating dilutions to fungal growth agar plates. The agar plates are then incubated and analyzed to determine if yeasts or molds are present, revealing the number of colony-forming units/g or ml.
If the sample is contaminated, the product should be further evaluated using a test like the USP <62> – Test For Objectionable Microorganisms, and possibly reformulated for better microbial protection. If it does not show the presence of fungal contamination, it can continue on to be tested for preservative efficacy (challenge testing), safety, and stability prior to distribution.