Like food and medicine, beauty products don’t last forever. Cosmetic chemists suggest looking for three key things to determine its expiration date and suggest ways to maintain its shelf life.

It’s tempting to use every drop of makeup or skin care product, especially if you paid a lot for it. Makeup does have an expiration date, though, and its lifespan may be shorter than you think.

Also, note if there’s an expiration date or PAO symbol on its packaging. Then, “you have an excellent estimation of how long the product will remain in its optimal form,” she said.