Unopened nail polish lasts up to 24 months when properly stored, according to Doug Schoon of Schoon Scientific. Essie Weingarten, founder of Essie Cosmetics, says that nail polish should last forever when stored properly. Ultimately, it’s up to the manufacturer to determine the shelf life.
Texture is one way to tell if a nail polish has gone bad. With time, old nail polish can become clumpy and thick, which makes it more difficult to apply evenly. To help nail polish last longer, it should be stored in a cool, dark place, away from heat and direct sunlight. Keeping the neck of the bottle clean using acetone also helps to extend usage.