The Challenge Test, also known as the Preservative Efficacy Test, is a mandatory requirement for most cosmetic products placed on the EU market and other regulated regions. This test confirms that a product remains microbiologically stable throughout its intended shelf life and Period After Opening.
However, not all cosmetic products require this testing. Certain products qualify for a Challenge Test Exemption when they are scientifically classified as microbiologically low risk. These products create conditions that do not allow microorganisms to survive or multiply.
The criteria for identifying low-risk products are defined in ISO 29621: Cosmetics — Microbiology — Guidelines for the risk assessment and identification of microbiologically low-risk products. Products that meet these criteria can demonstrate that the risk of microbial contamination is negligible.
ISO 29621 and the Low-Risk Product Classification
ISO 29621 provides a standardized framework for evaluating microbiological risk in cosmetic products. The guideline focuses on intrinsic product characteristics and external protective factors that prevent microbial growth.
To qualify for exemption, a product must clearly demonstrate that microorganisms cannot survive due to formulation chemistry, production conditions, or packaging design. This assessment must be based on scientific evidence rather than assumptions.
Compositional Factors That Support Exemption
The most common basis for a Challenge Test Exemption is the product’s formulation. Certain chemical environments do not support microbial survival or reproduction.
Low water activity is the most critical factor. Products with a water activity value of 0.75 or lower do not contain enough free water for microbial metabolism. Typical examples include lip balms, body oils, anhydrous powders, perfumes, and solvent-based nail products.
Extreme pH conditions also prevent microbial growth. Highly acidic products with a pH of 3.0 or lower, as well as highly alkaline products with a pH of 10.0 or higher, rapidly damage microbial cell structures. Chemical exfoliants, bar soaps, and hair relaxers often fall into this category.
High alcohol content provides another form of protection. Products containing 20 percent or more ethanol or similar alcohols act as self-preserving systems. Perfumes, hair sprays, and alcohol-based tonics are common examples.
Some formulations rely on ingredients that are inherently hostile to microorganisms. Strong oxidizing agents, high concentrations of aluminum salts, or organic solvents can inhibit microbial survival without additional preservatives.
Packaging and Production Factors
Beyond formulation chemistry, production methods and packaging systems can significantly reduce contamination risk.
Products filled at high temperatures, typically 65°C or higher, undergo a thermal process that eliminates vegetative microorganisms before sealing. This approach is common for hot-pour products such as lipsticks and solid sticks.
Protective packaging also supports exemption claims. Pressurized containers, single-dose units, and airless pump systems prevent air, fingers, and external contaminants from contacting the bulk product. By blocking contamination pathways, these packaging types significantly lower microbiological risk during consumer use.
Documentation and Regulatory Compliance
A Challenge Test Exemption is not automatic. Manufacturers must provide a detailed microbiological risk assessment to justify the exemption. This assessment must follow ISO 29621 principles and be included in the Product Information File.
The documentation must clearly explain why the product’s formulation, packaging, or manufacturing conditions ensure microbiological safety throughout its lifecycle. Regulatory authorities and safety assessors expect clear scientific reasoning supported by data.
When properly justified and documented, a Challenge Test Exemption confirms that the product is safe without requiring preservative efficacy testing. This final step is essential to maintaining compliance for microbiologically low-risk cosmetic products.
