How to review a cosmetic challenge-test report

A challenge-test report can arrive weeks after a sample leaves the lab. During that time, the development team may have changed a botanical, the pH target, or the preservative level. The favourable result still describes the sample that was tested; the team must decide how it applies to the formula now being considered for production.

Start by matching the report to the sample and formula version, then review the method, results, and any changes made since testing.

Testing the preservative system

A preservation efficacy test introduces a defined microbial challenge and assesses survival over time under the selected conditions. ISO 11930 addresses this test and the interpretation of testing and risk-assessment information when evaluating a cosmetic’s antimicrobial protection.¹

This differs from testing a sample’s microbiological quality before use. FDA’s methods discuss those microbiological findings separately from preservative efficacy.² A favourable challenge test also does not establish that the factory, filling equipment, or every production batch is free from contamination. FDA identifies several routes by which contamination can occur.³

The testing approach needs to fit the product. ISO 29621 provides guidance for assessing low microbiological risk; ISO 11930 excludes its preservation efficacy test from the scope for products assessed as low risk using the specified framework.¹⁴ Ask the microbiologist or safety assessor to establish the appropriate approach and its rationale.

Put the sample identity on the request

Give the laboratory the formula version, preparation or batch reference, sample identifier, preparation date, and relevant storage history. Supply the composition, intended use, and other information it requests. Agree the method, edition, reporting scope, and any planned modifications before work starts.

If the laboratory assigns its own identifier, retain the connection to yours. A product name alone is unreliable when several prototypes share it.

Read beyond the conclusion

For ISO 11930 work, neutralizer efficacy is one of the method’s considerations.¹ Ask the laboratory to explain a qualification before interpreting a low recovered count. Where the report is incomplete, keep the question and the laboratory’s response with it.

When the formula changed during testing

In a fictional project, version 3 of a moisturiser completes testing. Before the report arrives, version 4 introduces a different botanical and pH target.

The report remains evidence about version 3. A competent reviewer assesses the changes and decides what, if anything, is needed before relying on that result for version 4. A new version number alone does not determine the answer; the technical differences do.

Keep the version 3 report with the assessment of its relevance to version 4. Name any further work the reviewer requests. Retain unfavourable results too, with the investigation and the reason for any repeat test.

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