What Is Preservative Effectiveness?
A preservative efficacy study measures the formulation's preservative system's capacity to prevent microbial growth. Challenge testing is the core method; in a preservative optimisation study, variants prepared at different preservative concentrations are tested in parallel and the minimum concentration that provides efficacy is determined.
Purpose of Preservative Effectiveness
The purpose is to determine a preservative concentration that is both effective and not needlessly high. A high concentration creates issues with skin irritation and restriction limits, while a low one leaves microbial risk unaddressed.
Which Products Is Preservative Effectiveness Applied To?
- Water-containing cosmetic formulations
- Emulsion and gel structures
- Baby and sensitive-skin products
- Pharmaceutical topical products
- Multi-dose packaged products
In Which Sectors Is Preservative Effectiveness Used?
Standards Related to Preservative Effectiveness
- TS EN ISO 11930 (evaluation of antimicrobial protection)
- Ph. Eur. 5.1.3 (efficacy of antimicrobial preservation)
- USP <51> (antimicrobial effectiveness testing)
- TS EN ISO 29621 (guidelines for the risk assessment and identification of microbiologically low-risk products)
Preservative Effectiveness Conditions
- Number of variants
- Different preservative concentrations are tested in parallel during optimisation
- pH
- Preservative efficacy depends on pH; the formulation's pH is recorded
- Time points
- Enumeration on the days defined in the standard applied
Equipment for Preservative Effectiveness
- Microbiology laboratory and sterile cabinet
- Incubators and autoclave
- pH meter
- Colony counting system
Sample Requirements for Preservative Effectiveness
- A separate formulation variant for each preservative concentration
- Preservative-free control specimen
- Formulation, pH and preservative information must be provided
- Sufficient specimen quantity for each time point
Duration of Preservative Effectiveness
Each variant requires its own challenge-test duration, and even run in parallel, the study takes weeks. In optimisation studies, repeat cycles can extend the duration.
Preservative Effectiveness Procedure
- 1The preservative-concentration variants and the control are prepared.
- 2The pH of each variant is measured and recorded.
- 3Neutraliser suitability is verified.
- 4The variants are inoculated with the defined micro-organisms.
- 5Viable counts are performed at the time points.
- 6The minimum concentration that provides efficacy is determined.
Preservative Effectiveness Acceptance Criteria
The acceptance criterion is the logarithmic reduction values defined by time point in the standard applied (ISO 11930 or Ph. Eur. 5.1.3). The chosen concentration must also not exceed the maximum use concentration defined for that preservative in Annex V of (EC) 1223/2009.
Evaluation of Results
The result is formulation-specific: the same preservative shows different efficacy at a different pH or in a different emulsion structure. Carrying a preservative system that works in one product over to another without verification is therefore not safe. The test result alone does not establish compliance: (EC) 1223/2009 also requires appointing a responsible person, maintaining a Product Information File, having a qualified person carry out the safety assessment, and notifying the product to the CPNP. Laboratory data feeds into this file.
Preservative Effectiveness Report
- Formulation variants and preservative concentrations
- pH value of each variant
- Standard applied and test organisms
- Time-point counts and logarithmic reductions
- Minimum effective concentration determined
- Comparison against Annex V limits
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- (EC) 1223/2009 Cosmetic Products Regulation Annex V
Kozmetik Testleri — What Does This Testing Field Cover?
The section below describes the field that the Preservative Effectiveness test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Cosmetics testing shows that a product stays microbiologically safe throughout its use, delivers the performance it claims and contains no restricted substances. There is NO PRODUCT APPROVAL in this family: no authority approves a cosmetic product; responsibility rests entirely with the manufacturer and with the responsible person established in the EU.
This responsibility model shapes how the field works. Before the product is placed on the market a product information file (PIF) is prepared, a safety assessment (CPSR) is carried out and notification is completed. Inspection comes afterwards and asks for the file; if the file is incomplete the product is withdrawn from the market. Test reports form the evidence base of that file.
On the microbiological side there are two different questions and each is answered by a separate test. The CURRENT microbiological quality of the product is measured by enumeration and testing for specified microorganisms. The EFFECTIVENESS of the preservative system is examined by deliberately inoculating the product with microorganisms (challenge test): can the product resist repeated contamination throughout its use? A jar of cream is touched by a finger at every use; the preservative system must cope with that.
On the performance side, claim substantiation studies are carried out. For sunscreens, determination of SPF and UVA protection and measurement of water resistance are mandatory and are the basis of the value declared on the label. Evidence is also produced by in vivo or in vitro methods for claims such as moisturisation, appearance of wrinkles, hair care and colour retention.
On the chemical side, banned and restricted substances are screened: heavy metals, prohibited colorants, preservative concentrations, UV filter levels and contaminants such as nitrosamines. Products containing nanomaterials carry a separate notification obligation.
The BAN ON ANIMAL TESTING is the most defining constraint of the field. Animal testing cannot be carried out on finished products or ingredients, and a product tested on animals cannot be placed on the market. Alternative in vitro methods (reconstructed human skin models, cell culture based tests) are therefore at the centre of the field, and toxicological assessment rests largely on existing data, read-across approaches and in vitro results.
Stability and packaging compatibility studies determine shelf life and the period after opening (PAO). The interaction of the product with its packaging is also assessed: an active substance may migrate into the packaging, and substances that should not be present may pass from the packaging into the product.
On the process side, good manufacturing practice is demonstrated through ISO 22716; this is separate from product testing but a mandatory part of the file.
Method groups in this field
Microbiological quality
Enumeration of aerobic mesophilic bacteria, yeasts and moulds; testing for Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and E. coli.
Preservative efficacy
Resistance of the preservative system to repeated contamination by challenge test (ISO 11930).
Sun protection
In vivo SPF determination, in vitro UVA protection determination, water resistance and critical wavelength measurements.
Chemical analysis
Heavy metals, banned and restricted substances, quantification of preservatives and UV filters, contaminant screening.
Safety assessment
In vitro irritation and sensitisation methods, toxicological risk assessment, exposure calculations.
Stability and compatibility
Real-time and accelerated stability, packaging compatibility, PAO determination, sensory and physicochemical monitoring.
Commonly confused in this field
- There is NO CE marking on cosmetics; conformity is demonstrated through the PIF, the safety assessment and notification.
- The responsible person must be established in the EU; unless the exporter arranges this, the product cannot be placed on the market.
- Microbiological quality and preservative efficacy are different tests; a product that comes out clean may still have a weak preservative system.
- The animal testing ban covers ingredients too; animal test data generated for another market creates a problem of use.
- An SPF claim must be supported by measurement; a formulation change requires a new measurement.
- A change of packaging may require the stability and compatibility studies to be repeated.
Which decisions these results support
- The product information file and the safety assessment
- Verification of the preservative system design
- Substantiation of SPF and efficacy claims
- Determining shelf life and the period after opening
- Compliance with destination market restrictions for export
Related Tests
Frequently Asked Questions About Preservative Effectiveness
We want to reduce the preservative — how should we proceed?
Variants are prepared at stepped concentrations and tested by challenge testing in parallel. The lowest concentration that provides efficacy is identified, and the final formulation is re-verified at that concentration. Packaging type is also assessed together, since it affects risk.
Are natural preservatives sufficient?
They can be sufficient in some formulations, but this is not accepted as an assumption — it is demonstrated by testing. The efficacy of natural alternatives is more sensitive to pH and formulation structure than the classic preservatives in Annex V.