Ask a Scientist: Smelling your own breath

Question: Why can’t I smell my own breath?

This is probably one of my biggest gripes with my own body. You’re sitting there, existing as a regular ol’ human being, maybe with a few friends or acquaintances, talking about stuff. Could be about that test you just took, could be about plans for the weekend or that awesome movie you just saw. You know — normal stuff. Suddenly, one of them offers you a piece of gum. What are they trying to say? Are they just being nice or does my breath stink? There’s no way my breath stinks! Or does it? What’s wrong with me?!

Initially, this problem doesn’t make a whole lot of sense. Everyone’s breath has a smell, not necessarily a bad one but there’s something there. So why can’t we smell our own? Apparently, it doesn’t take much for our brains to recognize a scent. Sometimes it only takes 1 molecule out of a million. You know that saying, “It’s like trying to find a needle in a haystack?” Your nose finds the needle, effortlessly, every time. Seriously, the things we smell often can’t even be detected by other ways. I mean, we’re not as good as bloodhounds or anything, but humans can pick up on faint scents fairly easily. And every time we exhale, we release all sorts of stuff into air around us and a lot of that has a smell. So, what gives?

Turns out that, like most things related to our body, the problem lies in our brains. From blooming flowers to what’s coming out of the toilet, the scents our brains recognize are, unfortunately, not our choice. We continuously register smells, and some smells keep passing through our noses over and over again — especially what we’re exhaling all day long. Over time, our brains get tired of registering the same things, and they literally decide to ignore the smells until there’s a big enough change to get their attention. This process is formally known as “olfactory fatigue.” Basically, you’ve gone nose-blind to your own breath.

Wait, our breath's smell changes, you might say. Yeah, that’s totally true, but our brains constantly adapt to everything we sense. We might notice our stinky breath after a really garlicky meal because that caused a fast change in the smell. But most of the time, our breath’s smell changes slowly, and so our brain has enough time to tune it out. Since our brains are constantly adapting to slow-changing smells, we’re generally stuck with olfactory fatigue, and we’ll never really get to know what our breath smells like.

Have a question for Ask a Scientist or want to join our organization? Contact us by email at askasci@utk.edu or tweet us at @AskAScientistUT. Check us out on VOLink for sources used in this article and upcoming events we’ll be hosting.

Scott Satinover is a Bredesen Center Ph.D. student in bioenergy and biofuels and can be reached at ssatinov@vols.utk.edu.

Emily Clark is a Bresden Center Ph.D. student in nuclear energy and can be reached at ebuckman@vols.utk.edu.