Stability, Testing & Quality Control FAQs

Stability testing is not legally mandated for cosmetics, but it is considered a best practice for ensuring product quality, safety, and shelf life. Most contract manufacturers expect stability data to support reliable production and market release.

Stability testing should be performed after the final formula and process are set and before large-scale production begins. Early testing during development can identify risks, but formal stability studies should reflect the production-intended formula and packaging.

Preservative challenge testing (PET) is a laboratory test that evaluates whether a cosmetic product’s preservative system can control microbial growth over time. It is used to confirm that the formulation remains microbiologically safe under normal use and storage conditions.

The brand is ultimately responsible for ensuring that stability and PET testing are completed and documented. Testing may be performed by the contract manufacturer or a third-party lab, but oversight and decision-making remain with the brand.

Not all formulas require PET, but it is strongly recommended for products with higher water activity or greater microbial risk. The need for PET depends on formulation complexity, preservative strategy, and intended use, and should be assessed on a case-by-case basis.

If stability issues are found, the formula, process, or packaging may need to be adjusted and re-tested before production proceeds. Addressing issues at this stage helps prevent costly failures, delays, or recalls later in manufacturing or market release.

The system prevents failures by defining formulation architecture, processing logic, and operating ranges that account for real manufacturing conditions. Built-in documentation, substitution controls, and quality checkpoints reduce variability and catch issues before they reach production.