When I was an intern in the 1990's, I was on a team of old unix greybeards. Every 20 minutes or so, someone would have to go outside for a smoke break and they invited me along because that's where all the good design discussions would happen. Even today, I immediately recognize the smell of Marlboro Lights if I walk past a group of folks smoking outside.

I grew up in a town with a lot of feedlots, and I still don’t notice the smell when I visit. I definitely think your brain will block out background smells you grow up with. I wonder if that’s how people were able to live in medieval towns without sewers.