The stability test is essential to ensure that a cosmetic product retains its physicochemical properties, appearance, and safety throughout its shelf life. The formula is subjected to strictly controlled environmental conditions: temperature variations (cold, heat, thermal cycles), exposure to light (UV and visible light), relative humidity, and mechanical stress (agitation, vibrations). These stresses reproduce real-life situations encountered during transport, storage, or daily use, and allow us to verify that the product does not undergo any degradation or alteration in its performance.
Two complementary approaches are generally used:
- Accelerated stability – carried out over approximately three months, it uses high temperatures (often 40°C ± 2°C) and light/intensity cycles to simulate rapid aging. This method predicts long-term behavior, helps to choose the optimal packaging, and establish the minimum shelf life (MSL) date printed on the label.
- Stability in real-world conditions – Conducted over a period of up to three years, it keeps the product at temperatures and humidity levels similar to those encountered at points of sale and in consumers' homes. It confirms the results of the accelerated test and validates the final shelf life.
During testing, a range of parameters are measured at regular intervals: color, visual appearance, odor, pH, viscosity, density, volume, packaging integrity (leaks, cap deterioration), and any functional characteristics specific to the formula (UV filter effectiveness, antioxidant activity, active ingredient release). Any anomalies—phase separation, oxidation, loss of efficacy, or sensory alteration—are recorded and analyzed.
Compliance with these requirements is mandatory for the constitution of the DIP/PIF (Product Information File) and to meet the requirements of the’Swiss Ordinance on Cosmetics (OCos/OSAV) as well as the Regulation (EC) No. 1223/2009. By ensuring that the product remains stable, safe, and compliant throughout its shelf life, stability testing is a crucial step in bringing cosmetics to market in Switzerland and Europe.