When: The test must be done in at least two phases:
- during development of the product – after adding the preservative system;
- at the end of the stability testing and/or the of formulation compatibility test with the packaging material ( as an evaluation of the protection efficacy in intact, in-use or in ending cosmetic products).
How:The product is inoculated with a known quantity of different microbial pathogens (bacteria, molds, yeasts, etc).
- The micro-organisms used in the challenge test will be issued from official collection strains from many states in the EU to ensure reproducibility of the test (Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans). In-house microorganisms, found as contaminations in the products may be used for additional specific purposes of the challenge testing.
- The challenged product is incubated at a given temperature (22 °C ± 1 °C in the dark).
- Before the test, each cosmetic product is tested for its microbiological contamination
- Samples for determination of plate counts are taken after 0, 7, 14, 21 and 28 days Depending on the protocol used.
The microbial activity of preservatives or any other compound in the finished cosmetic must be ruled out in the challenge test by dilution, filtration, neutralizers or any other means.
The experimental performance of the microbial controls and the challenge tests must be laid down and validated by a microbiologist.