A: The inside of my refrigerator door, colorfully adorned with many little bottles of polish lined up along the top shelf, has often reminded me of a manicure salon (with anchovies, ketchup, and a half-empty jar of Grey Poupon). I've always suspected that keeping nail polish cold prevented spoilage, but I had no proof.
Suzi Weiss-Fischmann, executive vice president of OPI, claims that storing polish in the fridge will slow down the discoloration that happens as polish gets older. She suggests keeping the bottles upright, because if a bottle falls on its side it's harder to shake the pigments back together. The cosmetic chemist Mort Westman explains that refrigeration reduces solvent evaporation and pigment caking and settling.
But Mort, who must like to think of everything, expressed a concern. If you keep a highly flammable mixture (the polish) in a sealed box (the refrigerator) with a motor that could spark, what might happen if the bottle breaks or opens?
Bottom line: Though your polish will last longer in the refrigerator, it's probably safer to keep it in a cool, dry place away from sunlight—and potential sparks.