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.
The low-risk criteria in practice
ISO 29621 provides the framework for identifying products at low microbiological risk. Rather than granting a blanket exemption by product type, it describes the physico-chemical conditions under which microorganisms cannot realistically survive or multiply — and a formulation has to genuinely meet one of them.
The most commonly relied-on conditions are the absence of a water phase, a low water activity, an extreme pH at either end of the scale, and a high alcohol content. Anhydrous products such as oils, balms, butters, waxes, powders and pressed colour cosmetics fall into the first category; alcohol-based perfumes and toners fall into the last.
The critical distinction is between a product that contains no added water and one that is genuinely anhydrous in behaviour. Humectants such as glycerin, plant extracts supplied in a glycol or aqueous carrier, honey, and even hydrated raw materials can introduce enough available water to support microbial growth. Water activity, not the ingredient list, is what determines the outcome.
Documenting the exemption
An exemption is a conclusion reached by the safety assessor, not a decision the brand makes. It has to be recorded in the Cosmetic Product Safety Report and supported by evidence in the Product Information File, because “we did not run a challenge test” is exactly the kind of gap an inspection looks for.
A defensible justification usually rests on the full quantitative formulation showing there is no water phase or that alcohol content is sufficient, a water activity measurement where the case is not self-evident, the packaging format and how it limits contamination in use, and a reasoned statement from the assessor referencing the relevant ISO 29621 criterion.
Note that an exemption from preservative efficacy testing is not an exemption from everything. Stability and packaging compatibility testing still apply, and many assessors will still want microbiological testing of the finished product to confirm that manufacturing hygiene was adequate — the exemption concerns protection after opening, not cleanliness at the point of manufacture.
Where brands get exemptions wrong
Most failed exemptions follow one of a small number of patterns, and all of them are avoidable at formulation stage:
- Treating a product as anhydrous when an extract, humectant or hydrosol has introduced available water
- Applying the exemption to a product that is anhydrous in the jar but is used with wet hands or in the shower, such as a sugar scrub or cleansing balm
- Assuming the exemption carries across a range when only some variants are genuinely anhydrous
- Claiming it for a formulation whose alcohol content sits below the level needed to be self-preserving
The in-use water exposure case deserves particular attention. A cleansing balm or salt scrub may be perfectly anhydrous as manufactured, but if the consumer introduces water with every application, the assessor may well conclude that protection is required despite the formulation appearing to qualify. Where that risk exists, an anhydrous formulation with a broad-spectrum antimicrobial system, or packaging that avoids finger contact, is usually the better answer than pursuing the exemption.
Frequently asked questions
Who decides whether my product qualifies for an exemption?
The qualified safety assessor, as part of the Cosmetic Product Safety Report. It is a scientific judgement recorded in the file, not something the brand or the manufacturer can self-declare.
Does an exemption save much money?
It removes the cost of the challenge test and roughly 28 days from the timeline, which matters on a launch schedule. Stability and packaging compatibility testing still apply, so it reduces the testing burden rather than eliminating it.
Is an oil-based product automatically exempt?
Not automatically. It has to be genuinely free of available water and remain so in normal use. Oils with added botanical extracts in aqueous or glycol carriers, or products used with wet hands, frequently do not qualify.
Do I still need preservatives if the product is exempt?
Not necessarily for microbial control, but many anhydrous formulations still need an antioxidant to prevent oils going rancid. That is a stability issue rather than a microbiological one, and it is assessed separately.
