I have the condition called "Anosmia". It's a blessing to enter a public restroom and not experience the wave of smell that hits most people. But then when my wife puts on some lovely perfume, I am blind to that thrill.
Here's an account of the condition.
I'm not totally nose-blind. Some days I can see light or dark. How did it happen? I had a really bad sinus infection when I was about ten. That was the end of smells for me.