Key takeaways
- Accelerated testing predicts, real-time testing proves.
- Freeze-thaw catches phase separation that a constant temperature will not.
- Compatibility testing is about the pack, not the formula.
Stability testing answers one question: will this product still be acceptable to the customer at the end of its shelf life? Four test types are used together, and each answers a different part of that question.
Accelerated testing stores the product at 40 °C and 75% relative humidity for three to six months and extrapolates. It is fast and it catches most chemical degradation, but it cannot prove a three-year shelf life on its own.
Real-time testing stores the product at ambient conditions for the full claimed shelf life. It is the only test that actually proves the claim, which is why serious brands start it early and keep it running after launch.
Freeze-thaw cycling — typically three cycles between -10 °C and 25 °C — catches phase separation and crystallisation that a constant temperature misses. Emulsions that look perfect at 40 °C can break after two cycles.
Compatibility testing runs the formula in the actual pack. It catches interactions between the product and the container: leaching from a liner, corrosion of a pump spring, absorption into a PET wall. A formula that passes every other test can still fail here.
Reference: Internal QC protocols; ICH Q1A(R2) principles
