You can tell if a perfume is expired when the aroma becomes unpleasant.The smell turns slighly sour especially as the top notes oxidize. Secondly, expired perfume may result in skin irratation or in extreme cases, an allergic reaction. Another indication is discolouration [ of the juice ]. However, the good thing is that shelf life of fragrances are extending longer than before as many perfumers now use stabilizers and UV filters which makes molecules less sensitive to oxidation.
