Those plug-in "air fresheners" only work by covering up the unpleasant odor with a stronger "pleasant" odor. Pleasant to humans, that is. I use the liquid in the refill as a cat deterrent because they hate the smell.
I just had to jump in here. We had one plugged in a hallway socket and found my cat China sniffing the freshener, then turning in circles, like a rabid possum! She did it over and over, it was very scary. My husband ripped the freshener out of the socket and never let me buy one again!!
I think some cats are more sensitive to it than others. We use Bath & Body Works "Wallflowers" and Skeeter won't go near them, but Binx doesn't mind. It's the same when I put on lotion from B&BW...Skeeter gives me that squinty-eyed, pulled back head look and Binx couldn't care less.
Some air freshener products are known to cause cancer in lab animals, but I think those are mainly the spray kind b/c of of the chemical "Paradichlorobenzene".
But then there are some home freshening products like Febreeze that say on the bottle that it's approved (by the ASPCA?) for safe use around animals.
I bought some of the odor eliminators from Lowes that are made from volcanic rock. It comes in a pack of three or four 8x6 inch nylon fabric bags, that are screen like. They last for several months. Since we have the ginormous little box with the crate on the inside I just sat one in there. I also put one underneath our pool table because that is where all the puppy beds are. You do not notice any flower or spring fresh odor like you had sprayed something, you simply do not have odor. They are fantastic! We had tried many, many other products, this has been the best so far.