Cosmetics challenge test

A cosmetics challenge test, also known as a Preservative Efficacy Test (PET), is a mandatory assessment used to evaluate how effective a cosmetic product's preservative system is. It determines whether the product can resist microbial contamination during manufacturing, storage, and consumer use. This test is a key part of the Product Information File (PIF) and must be referenced in the Cosmetic Product Safety Report (CPSR) to ensure full regulatory compliance.

A challenge test is required to ensure that a cosmetic product remains safe throughout its shelf life. During normal use, products are exposed to bacteria, fungi, and other microorganisms from the environment and direct contact with the human body. The test verifies that the preservative system is strong enough to prevent microbial growth and protect both product quality and consumer health.

Cosmetics challenge testing is performed according to internationally recognized standards such as ISO 11930:2019 and USP <51> (United States Pharmacopeia). These standards define the testing procedures, microbial strains, and acceptance criteria to ensure consistent and reliable results across the cosmetics industry.

During a cosmetics challenge test, the product is intentionally contaminated with specific microorganisms under controlled laboratory conditions. The product is then monitored over time to assess how effectively the preservative system reduces or inhibits microbial growth. The test simulates real-life contamination scenarios to evaluate product safety and stability.

The standard challenge test typically includes five representative microorganisms that cover a broad spectrum of contamination risks:

• Staphylococcus aureus (gram-positive bacterium)
• Pseudomonas aeruginosa (gram-negative bacterium)
• Escherichia coli (gram-negative bacterium)
• Candida albicans (yeast/fungus)
• Aspergillus brasiliensis (mold/fungus)

These microorganisms are selected because they represent common contaminants that can affect cosmetic product safety.

The effectiveness of the preservative system is evaluated by measuring the reduction of microorganisms over time, typically after 7, 14, and 28 days. For a product to pass, bacterial counts must be significantly reduced by day 14 and remain low, while fungal counts must not increase throughout the testing period. These criteria ensure that the product remains safe during use.

A challenge test may not be required for microbiologically low-risk products, as defined by ISO 29621:2017. These include products that:

• do not contain water
• have extreme pH levels (below 3 or above 10)
• contain more than 20% alcohol
• include ingredients that create a hostile environment for microorganisms
• are produced under high-temperature conditions
• are packaged in airless pumps, pressurized containers, or single-dose units

However, any exemption must be clearly justified and documented.

Packaging plays an important role in reducing the risk of contamination. Products in airless dispensers, pump bottles, or sealed units are less exposed to microorganisms, which may reduce the need for a full challenge test. However, even with protective packaging, a proper risk assessment is required to ensure compliance.

If a product fails the challenge test, it indicates that the preservative system is not effective enough. In this case, the formulation must be adjusted — typically by modifying or strengthening the preservative system — and the test must be repeated. Only products that pass can be considered safe for market placement.

The challenge test is a critical component of cosmetic product safety assessment and is required for inclusion in the PIF and CPSR. It demonstrates that the product meets microbiological safety standards and complies with EU Cosmetics Regulation 1223/2009. Without it, most cosmetic products cannot be legally placed on the market.