The active ingredient breaks down rather quickly. Ironically, heat and light cause it to break down even faster. I would certainly get a new supply every year. The manufacturers don't bother to make it last too long, as that would hurt sales, Also, dipping your hands into it or on the top/dispenser means multiple exposures to bacteria therefore unless the preservative system is great (doubtful), it's probably chock-full of nasties. Like that moistureriser cream in that bottle in the back of your bathroom cabinet which is more or less green now...