Check the packaging for a PAO The PAO symbol contains a number and a letter, i.e. 12M, so this would indicate 12 months. It's typically 12M or 24M for polishes in my experience, so 12 months/24 months after opening, the product should be discarded.

Particles and dried out liquid, or a gooey, thick texture can all be signs that a polish may be past its expiry. If the polish has separated and you can't mix it together with a good shake, that's another sign you should throw it out.

“The main problem with using a polish that's been open for more than two years is that it won't yield as good of a user experience. It will probably be thick and hard to put on, and the color might have faded, too,” says Berry. “As polish gets old, it loses the ability to support an even, beautiful application.