Do makeup products need to be thrown away based on when it was opened or when it was bought?

I know that products like mascara, eyeshadow, concealer, foundation, etc have a specific length they last but say for example mascara lasts 4 months. Do I throw it away 4 months after i BUY it or after i OPEN it?Do makeup products need to be thrown away based on when it was opened or when it was bought?
It's definitely after you open the mascara. Once the package is opened, air and bacteria enter the tube, which is what can later cause eye infections. But when the package is unopened, you can keep it for as long as you like. :)Do makeup products need to be thrown away based on when it was opened or when it was bought?
The ';shelf life'; begins 4 months are you OPEN it. When you open it and use it, so comes the bacteria and germs that begin. But if you're product has an expiration date, that's when your product expires. In that case it doesn't matter if it hasn't been open and used yet. Good luck ^_^
The date that you opened the product is the date you should base the expiration date on.