People talk about how important it is to trigger all five senses in writing all the time.  True.  But how to do so in an interesting way?  I just read a fascinating article (The smell of virtue: Clean scents promote reciprocity and charity.) about the influence of scent on behavior - clean scents, in particular. First it cited a 2005 study that found people maintain "a cleaner environment while eating" if they can smell citrus cleaning products.  That's a pretty direct cause and effect - cleanliness begets cleanliness.  The author of this new study tried to draw a correlation between literal cleanliness and symbolic cleanliness, i.e., moral behavior.  He wanted to know if clean smells can make people more virtuous.

The answer appears to be yes.

In one experiment, volunteers were segregated into two equally clean rooms.  One had a neutral odor, however, while the other had been sprayed with citrus-scented Windex.  It smelled "clean".

All the volunteers then played a trust game.  I'm going to quote here:

"In a typical trust game the sender is given money that he can choose to keep or "invest" with an anonymous receiver.  Any money sent is tripled, and the receiver then decides how to split the tripled money.  For example, if the sender passes all of the money and the receiver reciprocates this trust by returning half of the tripled amount, both would be better off.  However, sending money can be risky if the receiver chooses to exploit the sender and keep all the invested money....

Al the participants in the current experiment were told they had been randomly assigned to play the role of hte receiver and that their ostensible counterpart had decided to send them the full amount ($4) which was now tripled to $12.  They had to decide how much money to keep or return to the sender.  Participants could exploit their counterpart by keeping all the money or they could honor the trust by returning some portion to the other party....

Participants in the clean-scented rooms returned significantly more money.

Significantly more money.  Wow.  Just because the room smelled like Windex.

The take home lesson for a writer is that smells need to be interactive.  Not just wallpaper.  Don't just ask yourself, "What does this place smell like?"  Try asking, "What smells here are important?  How does my character respond to those scents?"

Scent gives us access to our character's lizard brain - the realm below conscious awareness.  And that means we end up with more complex and more human characters.