Is Extended Use Of Fragrance Oils Harmful?

I've wondered if the oil fragrance diffusers of any type are actually dispensing an oil film that will eventually become sticky, adhere to furniture, cause environmental and health problems down the road...any opinions?
Of course, using it for a day won't do much, but what about using them for an extended period of time, like years?

Am basing this on the fact that they used to say to coat the inside of the nostrils with Vaseline to prevent colds, cut down on sore noses. Now research indicates that the stuff actually accumulates harmfully in one's lungs and is not expelled.

Holly from Richardson, TX

By cookwie