This is the part where I should be posting loads of interesting links on this subject, but I don't know how, lol. But here goes....
I was always curious about cigarette smoke but in my research I also came across material on scented candles, incense burners and aerosol cleansing/air freshener products.
There is a lot of readily available information on all of this. All you need to do is type in "toxic effects of".....and whatever it is you're interested in, ie cigarette smoke, scented candles, aerosol products etc etc..."on an aquarium."
It is certainly not a case of "oh yeah, they're all harmless". Take from all the information what you will. I guarantee you will think twice before using some "products" in the vicinity of your tanks.