Curious!? Why do we smell when we inhale but not when we exhale?


New Member
My husband just asked why we can only smell when we inhale! (dont ask he's a bit odd sometimes!) At first i started to say we do when we exhale but when i tried i cant! So i never noticed before but why is it that we only smell when inhaling? (stupid ass question i know but hey) its not important or relevent to anything but does anyone know the answer?


I think you can smell something when there are enough smell particles in the air without inhaling. Inhaling passes air over your smell receptors in your nose. Exhaling is expelling air from your lungs, and i don't think your lungs smell of anything.

Well that's my guess anyway ;)


New Member
its odd isnt it? hehe sorry for the complete randomness of the question my husband has a habit of asking me things like this (like i know! im not a doctor, yet!) It never occured to me before!! i would like to know the answer. maybe it has to do with the direction our smell receptors face in our noses? hmmm

Varied A

New Member
It's been a while since I studied any of this, but I think (someone correct me if I'm wrong), the chemicals stimulating the olfactory epithelium become trapped in the mucus lining on inhalation, therefore none make it down into the lungs. Because of that, there are none (or very few) make it down into the lungs and then back up again.


New Member
You can certainly 'taste' a good pungent belch but the gas being forced back up presumably doesn't go out through the nose... tell him to eat a pack of spring onions and down a litre of coke and then go keep his mouth tight shut for an hour... see if that makes a difference ;)


New Member
Your olfactory receptors are located in the upper portion of the nasal cavity. There are tens of thousands, each one designed to pick up a specific chemical scent. When we inhale these olfactory receptors are bathed in molecules of whatever it is that we might be smelling and are thus stimulated sending messages to the olfactory centre of the brain which combines all the individual messages to identify the smell.

As the receptors are high in the nasal cavity they require inhalation to get the smell to them. When we exhale things are forced in the opposite direction (the air kind of flows past them rather than through them). Of course, once the inhaled air has passed through the air passages and been effectively "filtered" by mucus and cilia in the nose, all those smelly chemicals should have been mopped up - so exhaled air shouldnt smell of much anyway! However it is not all limited to inhaling alone. Indeed most of our sense of taste is reliant on our sense of smell, its why food tastes so bland when you have a cold.

When you burp air from your stomach comes back up your oesophagus into your mouth and is expelled into the atmosphere. You wouldnt normally smell it as it comes back up, as it doesnt enter your nasal cavity (unless you have a cleft pallate perhaps) thus you only smell it when it is out in the air and you breathe it in again!
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New Member
I think it happens because of adaptation process. When we smell something there are more smell particles in the air than our lungs and when we sense it our smell receptors adapt with it and when we exhale some of that particles have absorbed by mucus and flagellum and don't sense anymore. But in burping smell particles are more inside and will sense. I'm sorry if i've done mistake in writing because my English is not good.