We red many articles on eyeshadow shelf life. It always states that, we can only consume it for 18 months after opening it and using it. I do not discount what I red in the articles, but based in my own experience, eyeshadow shelf life can last longer than 18 months.
Here are some tips which can prolong eyeshadow shelf life:
1. After using your eyeshadow, close it properly. Do not leave it open for too long, to avoid bacteria build up.
2. Always use clean applicators. When we use unclean applicators, there is bacteria build up. This is going to shorten eyeshadow shelf life.
3. Store it in a proper place and keep it covered at all times. (some users just leave it open on their dresser after using it.)
4. Avoid lending your eyeshadow to somebody else.
5. When there is an oil build up on the eyeshadow, get a Q tip and scrape the top then your good to go.