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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 (occuring everywhere) in nature just as bacteria are, cosmetics and personal care products are just as susceptible to contamination with them as with bacteria. The ability of these organisms to attack many cosmetic products is due in large part to their relatively versatile environmental requirements. Their pH requirement for growth is quite broad, ranging from pH 2 to greater than pH 9. Their growth temperature range is typically between 10 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 or not. 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. A 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 yeast or molds are present. If the sample is contaminated, the product should be further evaluated and possibly reformulated for better microbial protection. If it is clean, it can continue on to be tested for preservative efficacy (challenge testing), safety and stability prior to distribution.