does a bottle of cologne/eau de toilette, once opened, have a limited shelf life? i know i've kept some bottles for a very long time, but are you 'supposed' to do this?
Depends...I read once that the "filler" liquids (usually alcohol) in most fragrances (even the pricer stuff) will alter the essential oils of a cologne as time goes on. So, unless you can afford the pure esential oil stuff, I'd only shelve it for a year or two.
Apparently a bigger issue is whether the cologne has contact with air or worse, skin oils from splashing it on. A spray bottle kept in a dark cool place will last a very long time, while a splash kept under bright lights and used in contact with the skin will deteriorate much more rapidly.