Fragrance compounds are degraded by heat and light, even before you open the bottle. Off aromas may develop, turning that special occasion into an odoriferous affair. Lighter scents and less concentrated forms are most susceptible. Depending on what chemical compounds are formed, a fragrance could leave you red and scratchy. If something has been irritating your skin lately, it may be your perfume.
To keep perfume in its prime, protect it from its enemies. Keep it in comfortably cool and dry conditions, away from heat sources and direct sun. Don't keep perfume in the bathroom, where humid air can infiltrate the bottle. If heat and humidity are inescapable -- in the Florida Everglades in July, for instance -- keep it in the refrigerator. The crisper is specially designed for reduced humidity. It's also a good idea if you need to put an open bottle in storage for a few months -- to keep a summer fragrance during the winter, for example.
Buy perfume in spray bottles, if possible. They let in less air than ordinary bottles, which reduces evaporation, contamination and chemical reactions. To transfer perfume from a bottle to an atomizer, first rinse the atomizer with rubbing alcohol to remove the old fragrance. Let it stand a few minutes, then rinse with water and air dry.
Under optimal conditions, an unopened bottle of perfume will keep for up to 18 months. Bu who could buy a new perfume and wait that long to use it?