Shelf life in cosmetic products is a period of time that shows how long the product can be used safely and effectively from the date of manufacture. A series of tests are performed on cosmetic products to determine the shelf life. The purpose of these tests is to evaluate the physical, chemical and microbiological stability of the product and to ensure that the consumer is safe.

Let's take a look at the shelf life determination tests in cosmetic products:

1. *Accelerated Stability Test:* The product is stored at high temperature (eg 40°C - 50°C) for a certain period of time. This causes the product to age faster than its normal shelf life. This test is used to evaluate the stability of the product against temperature changes.

2. *Microbiological Stability Test:* After the product is contaminated with various microorganisms, it is checked whether these microorganisms can multiply in the product.

3. *Physical and Chemical Stability Test:* The color, consistency, pH value and other physical and chemical properties of the product are checked at regular intervals.

4. *Packaging Stability Test:* It is evaluated whether the product interacts with its packaging and whether the packaging protects the product.

5. *Real-Time Stability Test:* The product is stored for a certain period of time (at room temperature or at a certain temperature) in real time. The features of the product are checked at regular intervals.

An expiration date (SKT) is added to the product label based on shelf life test results, or a symbol indicating how long the product can be used after opening (eg "12M" - means the product must be used within 12 months after opening).

Determining the shelf life of cosmetic products is a critical step to ensure the quality of the products and the safety of the consumer. That's why these tests are tightly regulated by regulatory agencies and industry standards.