Challenge testing is mandatory for all cosmetic products for which a risk of microbial growth during normal conditions of storage or use is identified.
Preservatives are included in most finished cosmetic product formulations to protect them from microbiological contamination during normal consumer use. The purpose of the challenge test is to verify the reliability of the preservative system during the shelf and usage life of the cosmetic product
While there are different challenge tests protocols, similar methods are described in the EU Pharmacopeia and US Pharmacopeia. These protocols differ one from the other in the detailed procedures, test organisms, criteria for passing the test and the requirements for validation.
Concerning microbiological susceptibility there are difference between three product categories:
- Low microbiological risk products (e.g., products with alcohol content >20%, products based on organic solvents, high/low pH products), for which neither a preservation challenge test nor microbiological quality tests in the finished product are necessary. Nevertheless, scientific justification should be provided detailing the reason why the product is low microbiological risk.
- Single use products, and products which cannot be opened, for which only microbiological quality tests in the finished product are necessary;
- All other products, for which both a preservation challenge test and microbiological quality need to be performed
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.
The antimicrobial properties of the product are acceptable 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.
The conclusions report of Challenge Test shall contain:
- Identification of the lab conducting the testing
- Identification of the product
- Packaging material used in the test
- A description of the methodology used – the protocol
- Study conditions
- The result of the study.
- The signature of the person responsible for the study