Testing the effectiveness of preservatives in cosmetic products (Preservative Efficacy Test): Guide to ISO 11930
Cosmetic products offer an extremely favorable breeding ground for the growth of microorganisms due to their content of water, oils, proteins and other nutrients. If a cream, lotion or shampoo is exposed to contamination by bacteria, yeasts and mold on the way from manufacture to the consumer, this can spoil the product, produce unpleasant odors and skin infections. In order to exclude this risk, the effectiveness of the preservatives added to the formulations must be scientifically proven. This is where the Preservative Efficacy Test (PET), also known as the Challenge Test, comes into play.
The preservation efficacy test assesses how resistant the preservation system of a cosmetic product to microbial contamination that can occur during manufacture or when used by the consumer. This test is carried out as part of the internationally recognized standard ISO 11930 and provides important data for the safety assessment report (Safety Assessment Report - SAR) of cosmetic products.
What is the preservation efficacy test and why is it required?
The test for protective effectiveness is based on the principle that the product is specifically inoculated (inoculated) with certain microorganism strains and the decrease in the number of microorganisms is monitored at certain intervals. The main goal of the test is to prove that the product remains microbiologically safe throughout its shelf life and during consumer use.
The requirements for the conservation effectiveness test can be summarized as follows:
- Legal obligation: The EU Cosmetics Regulation (EC) No 1223/2009 and national legislation stipulate that products must be microbiologically safe.
- Product safety: A product with insufficient preservation system represents a risk of infection for the consumer.
- Optimization of the recipe: The test results enable the concentration and combination of preservatives to be optimized.
- Determination of the shelf life: The effectiveness of the preservatives is directly related to the shelf life of the product and the "lasting shelf life after opening" (PAO).
- Compatibility with the packaging: Different types of packaging (airtight pump, crucible, tube) influence the risk of contamination.
ISO 11930 standard and testing principle
ISO 11930 is an internationally recognized standard for assessing the antimicrobial effectiveness of cosmetic products. This standard determines how the test is to be carried out, which microorganism strains to use, which inoculum concentration is to be used and which acceptance criteria apply.
Test principle
The test includes the following steps:
- Sample preparation: The product is transferred to suitable containers under sterile conditions.
- Inoculation: Each microorganism strain is added separately to the product sample (usually at a concentration of 10⁵-10⁶ cFU/g).
- Incubation: The seeded samples are incubated at a fixed temperature (usually 20-25°C).
- Sampling: Samples are taken at certain intervals (0, 7, 14, 28 days).
- Count: At each point in time, the number of living microorganisms (LOG decrease) is determined.
- Evaluation: The results are classified in categories A, B or C according to the acceptance criteria of ISO 11930.
Microorganism strains used
ISO 11930 provides for the use of the following standard strains:
- Bacteria: Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 8739), Pseudomonas Aeruginosa (ATCC 9027)
- Yeast: Candida albicans (ATCC 10231)
- Mold: Aspergillus brasilissis (ATCC 16404)
In some cases, additional strains (e.g. Burkholderia Cepacia) can also be tested, depending on the purpose of the product.
ISO 11930 acceptance criteria: Categories A, B and C
ISO 11930 evaluates the test results in three categories. Category A stands for the highest preservative effectiveness, category C for the lowest effectiveness.
| Category | Bacteria (log decrease) | Yeasts and molds (log removal) | Valuation |
|---|---|---|---|
| Category A | Day 7: ≥ 3 log Day 14: ≥ 3 log Day 28: ≥ 3 log + no increase | Day 7: ≥ 2 log Day 14: ≥ 2 log Day 28: ≥ 2 log + no increase | High preservation effect, sure |
| Category B | Day 14: ≥ 3 log Day 28: ≥ 3 log + no increase | Day 14: ≥ 1 log Day 28: ≥ 1 log + no increase | Acceptable protective effect |
| Category C | Day 14: ≥ 2 log Day 28: ≥ 2 log + no increase | Day 14: ≥ 1 log Day 28: ≥ 1 log + no increase | Low effectiveness, risk assessment required |
USP <51> und andere Normen
In addition to ISO 11930, standards such as USP <51> (test of antimicrobial efficacy according to the US Pharmacopoeia) or EP 5.1.3 (European Pharmacopoeia) can be used. USP <51> was specially developed for pharmaceutical products and is also valid for cosmetic products as a reference.
Die wesentlichen Unterschiede zwischen USP <51> und ISO 11930:
- Acceptance criteria: USP <51> defines different log acceptance criteria for bacteria and fungi.
- Categories: USP <51> Classifies products into categories 1, 2 and 3.
- Scope: While USP <51> is primarily geared towards pharmaceutical products, ISO 11930 applies specifically to cosmetics.
Factors affecting the test results
The results of preservative efficacy tests can be influenced by various factors. These factors must be taken into account in the test design:
- Formulation matrix: The water content, the pH, the oil phase and the emulsifiers influence the efficacy of the preservative.
- Packaging type: Various packagings such as airtight pump bottles, crucibles or tubes change the risk of contamination.
- Concentration of the preservative: Too low a concentration causes the test to fail.
- PH value: Some preservatives (e.g., phenoxyethanol) are more effective in certain pH ranges.
- Inoculum concentration: The inoculum amount determines the difficulty level of the test.
- Incubation temperature: The growth of microorganisms is temperature dependent.
Accredited Services to Check Preservation Efficacy with Nano Test
The microbiological safety of your cosmetic products and the effectiveness of your preservation system are crucial for both consumer health and the reputation of your brand. Nano-Test is a reliable partner in the cosmetics industry with its comprehensive services to test the effectiveness of preservatives in ISO/IEC 17025-accredited laboratories.
Description of Nano-Test Services
NANO-TEST offers Tests on the efficacy of preservatives (preservative efficacy test) for cosmetic products. Our analyzes are carried out in full compliance with the ISO 11930 and USP <51> standards.
Our service portfolio:
- ISO 11930 Challenge Test: Rating according to categories A, B and C, measurement of log drops at times 0, 7, 14 and 28 days.
- USP <51>-compliant test: Alternative standard for pharmaceutical and cosmetic products.
- Inoculum preparation and validation: Preparation of fresh cultures of standard strains (ATCC) and concentration review.
- Neutralization Validation: Validation of the neutralization and dilution efficiency specific to your product matrix.
- Specific strain tests: Examination of additional microorganism strains depending on the purpose of the product.
- Report: The results are presented with log drop values, categorization and graphical analysis.
All of our analyzes are presented in the form of reports audited and whose data integrity (according to the ALCOA+ principles) is guaranteed. Our goal is to ensure the acceptance of your products in global markets while ensuring the highest level of consumer safety.
Benefits of the Nano-Test protective efficiency test:
- Accredited infrastructure: Internationally recognized test reports with ISO/IEC 17025 accreditation.
- Norm conformity: Complete conformity with ISO 11930, USP <51> and EP 5.1.3 standards.
- Quick results: Reporting within 5-7 working days after a 28-day incubation period in standard challenge tests.
- Specialist team: A team with experience in the fields of microbiology and cosmetic law.
- Solution from a single source: germ counting, pathogen detection and challenge tests - all under one roof.
The test on the effectiveness of the preservation system for cosmetic products is not only a legal obligation, but also an indispensable quality assurance instrument to protect consumer safety and brand reputation. Challenge tests conducted in accordance with ISO 11930 standards scientifically demonstrate the effectiveness of your product's preservation system and ensure that it is recognized in international markets.
With its accredited laboratory infrastructure, its team of experienced microbiologists and its in-depth knowledge of current standards, NANO-TEST fully meets the requirements of cosmetics manufacturers for preservative effectiveness tests. Collaborate with Nano-Test to increase the safety of your products and accelerate their market launch.