The Purpose of conducting stability and micro testing on all new formulas is to ensure the integrity of the beauty product over time. There are two tests to ensure that integrity. This testing is done once the formula has been approved and before the manufacturing. These tests will need to be repeated if the formula has been changed in any way. The two tests are micro challenge and stability.
The Micro challenge test is the most important of the two tests. It will test the efficacy of the preservative system in the beauty product. The preservatives prohibit growth of bacteria, yeast and mold. The Micro challenge test will show that the preservative will effectively work for at lest three years.
Scientific Committee, Consumer Products, opinion on Challenge Testing for Cosmetics, “the manufacturer must guarantee the efficacy of the preservation of his cosmetic products experimentally by Challenge Testing. However, as no legal nor universal Challenge Testing method is available today, it is up to the manufacturer to decide on the details of the test to be used.”