Preservative Efficacy Testing, aka PETs or Challenge Testing, is performed to evaluate your product's antimicrobial properties. To perform this test, the lab introduces a known quantity of a known species of organism into the product and measures those organisms' viability over a 28 day period. A successful test will yield no less than a two-log reduction in counts from day zero (0) to day fourteen (14), and no increase in counts from day fourteen (14) to day twenty-eight (28).
While PET's are great at helping you understand your product's antimicrobial properties, this test is not a Stability Test or Shelf Life Test.
Stability and Shelf Life testing measures the concentration of the active ingredients in the product. It also monitors its organoleptic properties such as color, smell, taste, viscosity, appearance, and efficacy over time. This test is performed by collecting enough finished product samples for the duration of the testing, placing half of the samples in a stability chamber, set at 40 degrees C and 75% relative humidity. The other half of the samples are placed in a controlled environment mimicking the natural conditions of the target market in which the products are to be sold. The former is known as the accelerated shelf-life test, and the latter the real-time shelf-life test. A profile of physical characteristics and actives tests is conducted according to your label claims, at 0, 3, 6, 9, 12, 18. 24, and 36 months. The real-time samples are pulled according to these months, and the accelerated portion of the tests will occur based on the Arhenius formula, which dictates how many days in the chamber are equivalent to real-time days.
The purpose of the stability study is to learn how the product fairs over time and how long you can expect the product to meet its quality specifications.