It's known as olfactory adaptation. The body releases chemicals to help neutralize odors that you are frequently exposed to. So if you regularly wear too much perfume, or you live near a factory or something, you become desensitized to the smell.
I'm familiar w/the concept and I have experienced it. (Esp. that living near a factory business - whenever I go to visit my parents, I'm shocked by the strength of the smell from the paper plant, b/c while it surely stank when I was a kid, it just never seemed that STRONG.) But even so I always seem to be even more sensitive to my own scent than anyone around me. (Then again, I also always seem to be more sensitive to everyone else's scent than they are, too.)