I once heard George Carlin talking about hats. To paraphrase what he said – Isn’t it interesting that when you put on a hat you are, at first, really aware that it’s on your head and then after awhile you don’t even realize you have it on. But when you take it off, it still feels like you are wearing it. It’s the same with smells. Everytime you first get into a relatively new car, it has that “new car” smell. Then after riding in it for a while you don’t smell it. But the next time you get in, there it is again! It’s a phenomenon called habituation.
habituate – To accustom by frequent repetition or prolonged exposure. (dictionary.com)