The appearance of the Smell column is timely. Just the other day, my 6 year old asked me “Daddy, why can you only smell when you breathe in and not when you breathe out?”. I was at a complete loss to explain this phenomenon.
Does it have something to do with the shape of the olfactory receptors?
Assuming you’re referring to this article: http://www.straightdope.com/mailbag/msmells.html
If you could smell while you were exhaling, you’d be smelling yourself. Thankfully, olfactory fatigue makes it so we don’t get a fresh whiff of lung every time we breathe out.
On the other hand, one of the ways I can tell if I’ve got a respiratory infection is a smoky or burnt smell when I exhale.
My WAG would be that you can smell when you breathe out. But testing it would require putting something fragrant in my airways so I won’t do that.
Oh, I thought of a different way to test it. Hold your breath and pinch your nose. Walk to your pre-prepared source of fragrance and take a deep breath through your mouth. Walk elsewhere, preferably somewhere with good ventilation. Breath out through your nose and see if you can smell whatever it was.
For proper scientific rigour someone should pick the fragrance at random and there should be multiple trials. I’d do it, but I have a cold.
For what it’s worth, I always know when I’m getting a sinus infection because I get a “baking bread” note on my exhalations.
As the proud owner of a former six year old I can answer this question easily.
“Son, you smell all the time.”