Also referred to as Microbial Challenge Test or Preservation Efficacy Test (PET)
Oxford Biosciences has a dedicated on-site laboratory and microbiologist to ensure compliance with acceptable testing standards. We comply with ISO 11930:2019 testing procedures: Cosmetics — Microbiology — Evaluation of the antimicrobial protection of a cosmetic product. This ISO standard is a reference method that is used to evaluate the preservation of a cosmetic formulation. It applies to cosmetic products in the market place.
We charge £155 per cosmetic product. Your product is challenged, incubated, examined at 7, 14 and 28 days, and the final results are then emailed after the requisite 28 days.
Both “Preservative Efficacy Testing” and “Microbial Challenge Testing” are commonly used phrases in the field of microbiology and cosmetic/pharmaceutical industries. However, “Preservative Efficacy Testing” is more commonly used than “Microbial Challenge Testing” in the context of evaluating the ability of a product to resist microbial growth over time. This is because the primary objective of this type of testing is to determine the effectiveness of the preservative system in a product, rather than just exposing the product to a microbial challenge. However both terms are often used interchangeably in literature and discussions related to microbiological testing.
The Challenge Test
The efficacy of the preservation of a cosmetic product under development has to be assessed experimentally in order to ensure microbial stability and preservation during storage and use. This is done by challenge testing. The latter is mandatory for all cosmetic products that, under normal conditions of storage and use, may deteriorate or form a risk to infect the consumer.
A challenge test consists of an artificial contamination of the finished product, followed by a subsequent evaluation of the decrease in contamination to levels ensuring the microbial limits established. The evaluation of the preservation of a cosmetic formulation is based on inoculation of the product with calibrated inocula (prepared from relevant strains of micro-organisms). The number of surviving micro-organisms is measured at defined intervals during a period of 28 days. For each time and each strain, the log reduction value is calculated and compared to the minimum values required for evaluation. Using ISO 11930:2012 the microorganisms used in the challenge test may be issued from official collection strains from any state in the EU to ensure reproducibility of the test and are:
- Pseudomonas aeruginosa ATCC®9027TM2
- Staphylococcus aureus ATCC®6538TM
- Candida albicans ATCC®10231TM
- Aspergillus brasiliensis (previously A. niger) ATCC®16404TM
- Escherichia coli (ATCC No. 8739)
The responsible person must guarantee the efficacy of the preservation of their products experimentally by challenge testing.
A product passes the challenge test if a significant decrease or no increase in viable count of micro-organisms is seen:
- A 2 log reduction in the microorganisms counting after 14 days compared to that at the beginning
- A 0.5 log reduction in the microorganisms counting after 28 days compared to that after 14 days.