When products are sold, opened and start being used, they have to be able to retain their microbiological stability. The efficacy of the preservative system has to therefore be tested before market launch and this is done through the challenge test, also known as the preservative efficacy test (PET).

At the beginning of the challenge test, cosmetic products are artificially contaminated with known strains of microorganisms (usually Pseudomonas aeruginosa, Staphylococcus aureus, Aspergillus brasiliensis, Escherichia coli and Candida albicans), after which the contaminations levels are monitored during the following four weeks. In order to pass the challenge test, contamination levels have to be sufficiently reduced.

The challenge test is mandatory for all cosmetic products that, under normal conditions of storage and use, may deteriorate or form a risk of infecting the consumer. Certain microbiologically low-risk products don’t have to undergo a challenge test but any such lack of challenge test has to be duly justified.

We can perform the challenge test either according to ISO 11930:2012 or USP 51.