Preservative Challenge Testing (ISO 11930): When You Need It and How to Evaluate Pass/Fail

Preservative Challenge Testing (ISO 11930) is a critical step for skincare brands sourcing formulations that must remain safe and stable throughout their shelf life. Understanding when the test is required—and how to interpret pass/fail results—helps buyers verify microbial protection, avoid product recalls, and maintain compliance in global markets.

What Preservative Challenge Testing Shows

The ISO 11930 method evaluates how effectively a cosmetic formulation resists contamination by microorganisms once opened, during use, or through accidental exposure. It measures microbial reduction over time after deliberate inoculation with known bacteria, yeast, and mold strains.

• Purpose: Confirm preservative system adequacy and formulation safety.
• Applies to: Water-based creams, serums, emulsions, and masks—especially in multi-use packaging.
• Key organisms tested: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, Aspergillus brasiliensis.

When You Need It

Not every cosmetic requires ISO 11930 testing, but it becomes mandatory in specific formulations and markets:

• High-water content formulas (emulsions, gels, toners) intended for extended shelf life.
• Products in wide-mouth jars or droppers with repetitive consumer exposure.
• Reformulations that alter pH, surfactant system, or preservative load.
• Claims driving formulations—such as “preservative-free,” “minimal preservative,” or “natural”—requiring alternative efficacy validation.
• Regulatory expectation for EU, UK, and several APAC markets referencing ISO 11930 in Product Information Files.

Testing Process Overview

1. Sample inoculation: Known microorganisms are introduced into the test sample.
2. Incubation period: Samples are stored under controlled temperature and humidity.
3. Microbial count monitoring: Reductions are measured at day 7, 14, 28, and 90 (if needed).
4. Assessment: Results are compared to acceptance criteria (A or B levels under ISO 11930).

Sample Table – ISO 11930 Acceptance Criteria

How to Interpret Pass/Fail Results

• Pass (Criteria A): Formula demonstrates robust preservative performance under simulated use.
• Pass (Criteria B): Acceptable, but may need justification in the Product Information File or safety assessment.
• Fail: Microbial growth exceeds threshold—requires reformulation, pH adjustment, or alternative preservative system.

Buyer Verification Checklist

When evaluating finished formulas or working with OEM/ODM labs, request these items to confirm preservative testing readiness:

• Full ISO 11930 report with all test organisms and log-reduction data.
• Sample identifier code matching batch record or stability sample ID.
• Microbiological laboratory accreditation (ISO/IEC 17025 preferred).
• Formulation sheet showing preservative concentration, pH, and water activity (a_w).
• Packaging compatibility data—especially for air-contact designs.

Practical Tips for Sourcing Managers

• Lock formula before packaging tests: Changing container or closure may alter microbial load or preservative exposure.
• Coordinate testing with stability study: Align challenge testing schedule with ambient and elevated stability runs.
• Keep evidence organized: Maintain report copies and lab COAs in your quality dossier; inspectors request these first.
• Clarify “clean beauty” claims: Reduced preservative usage must still demonstrate microbial control to pass audit.

Common Buyer Scenarios

• **Private‑label launch:** Request manufacturer’s latest ISO 11930 report for the chosen base formula.
• **Customized formulation:** Conduct new testing after ingredient or fragrance changes affecting pH.
• **Region change (e.g., US → EU):** Confirm report format and organism panel align with EU Cosmetic Regulation Annex I requirements.

FAQ

1. How often should challenge testing be repeated?
Retesting is advised whenever the preservative system, raw material supplier, or packaging type changes, or every 3 years for regulatory renewals.

2. Can “preservative-free” products pass ISO 11930?
Yes—if the system relies on hurdle technologies (low water activity, acidic pH, chelating agents) and demonstrates equivalent microbial control.

3. Is PET (Preservative Efficacy Test) the same as a challenge test?
They refer to the same methodology; PET is the common term used interchangeably with preservative challenge testing.

4. How do I know if Criteria B is acceptable?
Criteria B may be accepted with documented risk reasoning from a cosmetic safety assessor, showing consumer safety is not compromised.

5. Can results differ between labs?
Minor variations can occur due to inoculum preparation and lab procedures, which is why ISO/IEC 17025 accreditation ensures comparability.

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Hi, I'm Alex Zong, hope you like this blog post.

With more than 20 years of experience in OEM/ODM/Private Label Cosmetics, I'd love to share valuable knowledge related to cosmetics & skincare products from a top-tier Chinese supplier's perspective.