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 11930:2012 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 £150 per cosmetic product. We are the only lab that provides interim results to inform you how your product is progressing through the challenge, as well as the final results after the requisite 28 days.
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. 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
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.