--- title: "Preservative Challenge Testing (PET)" description: "Test preservative efficacy with a microbial challenge test." image: "https://cosmetic-labs.com/wp-content/uploads/preservative-challenge-service-1200x1200-1.webp" --- # Preservative Challenge Testing (PET) > Test preservative efficacy with a microbial challenge test. Source: https://cosmetic-labs.com/services/in-vitro-testing/cosmetic-quality-testing/preservative-testing/preservative-challenge Created: 2025-03-17T20:36:19+00:00 Modified: 2026-10-25T09:07:08+00:00 Author: Emilie SCHOL Preservative Challenge Testing (PET) | Cosmetic Labs ## What is Preservative Challenge Testing (PET)? A report on control of deliberately introduced microorganisms. ### Why do you need this service? Request it for a new formula or when a change may affect preservation, such as altered pH, preservative concentration or raw materials. The need for testing and retesting should follow a documented risk assessment, not an assumed universal annual schedule. ## Be the first company on this service page No published company profiles are linked to Preservative Challenge Testing (PET) or its more specific services yet. Explore the service categories or add an explicitly supported capability to your company profile. [List your company](https://cosmetic-labs.com/account/companies/new) Definition ## Preservative challenge testing The laboratory selects a method appropriate to the product, intended use and specification. ISO 11930 addresses antimicrobial protection of cosmetics. USP chapter 51 or Ph. Eur. 5.1.3 may apply in other product or specification contexts, but these methods are not automatically interchangeable. ### Protocol and recovery controls The agreed method defines the challenge organisms, inoculation procedure, storage conditions, sampling points and acceptance criteria. Counts are assessed by organism and time point rather than against invented limits for broad product categories. Neutralization and microbial recovery must be suitable for the formula. If residual preservative continues to inhibit organisms during counting, an apparently favorable result may reflect analytical interference rather than the product’s actual performance. ### Reporting the result The report should identify the tested sample, method, controls, counts and interpretation against the selected criteria. Deviations and method limitations should be explicit. A result applies to the formula and conditions tested, not automatically to later reformulations, different packaging or all foreseeable consumer handling. Challenge testing contributes to the preservation assessment. It does not replace manufacturing hygiene, routine microbiological quality control or evaluation of protection as the product ages. Applications ## Deliverables and limitations Request a report identifying the sample and method version, suitability checks, initial and subsequent microbial counts, calculated log reductions, deviations and the applicable conclusion. Any qualified result or additional protective factors used in interpretation should be explained. Agree sample requirements and laboratory scheduling directly rather than assuming a standard turnaround. A satisfactory challenge result supports the preservation evidence for the tested sample and conditions. It does not establish shelf life, rule out manufacturing contamination or guarantee protection during every consumer use scenario. Combine it with formula, packaging and use-context review when a broader preservation decision is required. Antimicrobial activity of a cosmetic active is a separate testing question. ExplorationLearn more about Microbiological TestingAssess cosmetic microbiological quality through challenge testing, contamination screening and preservation studies, with each test question defined. Explore another Microbiological Testing page on cosmetic-labs.com. #### [Microbial Contamination Screening](https://cosmetic-labs.com/services/in-vitro-testing/cosmetic-quality-testing/preservative-testing/contamination-screening) Check cosmetic raw materials or finished samples for existing microbial contamination, with counts and organism results matched to your specification. [Check this service](https://cosmetic-labs.com/services/in-vitro-testing/cosmetic-quality-testing/preservative-testing/contamination-screening) #### [Preservation System Efficacy Assessment](https://cosmetic-labs.com/services/in-vitro-testing/cosmetic-quality-testing/preservative-testing/preservative-efficacy) Evaluate the complete preservation strategy for a cosmetic product, combining challenge-test evidence, formula properties, packaging and intended use. [Check this service](https://cosmetic-labs.com/services/in-vitro-testing/cosmetic-quality-testing/preservative-testing/preservative-efficacy) #### [Microbiological Stability During Storage](https://cosmetic-labs.com/services/in-vitro-testing/cosmetic-quality-testing/preservative-testing/microbiological-stability) Assess microbial condition and preservation performance as a cosmetic product ages, with sampling and storage conditions matched to the study question. 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