How can one determine if nail polish is old or expired?

When evaluating whether nail polish is old or expired, a thick consistency is a clear indicator of degradation. Over time, nail polish can undergo changes in its formulation, leading to evaporation of solvents and a thickening of the remaining product. This thickening can make the polish difficult to apply smoothly and evenly, indicating that it may no longer perform as effectively or provide the desired finish.

In contrast, a strong fragrance may not necessarily indicate age, as some polishes can still smell potent despite being older. A more vibrant appearance is often a sign of fresh polish, as old polish typically loses its luster. Lastly, bubbling when shaken can occur in both old and new polishes and thus is not a reliable indicator of age. Therefore, thick consistency is the most definitive sign of nail polish that may be past its prime.