The fact that we rarely catch a whiff of our own breath seems fishy. For one, our noses are only a philtrum’s length away from our mouths. We also don’t have any trouble inhaling other people’s stale carbon dioxide, even with a solid few feet between us.
Though we don’t yet have a decisive scientific explanation for this olfactory phenomenon, there’s no shortage of promising theories. According to BreathMD, it could be that we became so accustomed to smelling our own breath that we simply don’t notice its odor anymore—similar to the way we can’t detect our own "house smell." This kind of habituation doesn’t just inure us to unpleasant aromas, it also leaves our noses free to focus on unfamiliar odors in our environment that could alert us to danger.
As HowStuffWorks reports, another hypothesis suggests that we’re more conscious of other people’s halitosis because breath released when speaking is different than breath released when exhaling regularly. All the tongue movement that happens when someone talks could push odors from the back of their mouth out into the air.
But if that’s true, it seems like you’d be able to smell your own breath—at least when you’re the one doing the talking. Which brings us to the next and final theory: That your bad breath dissipates before you get a chance to inhale it. When someone else exhales, you’re inhaling their air almost simultaneously. When you exhale, on the other hand, you have to wait until you’ve reached the very end of your expiration before breathing back in again. By that time, the malodorous particles may have already dispersed.
Even if you’re blissfully unaware of how your own breath smells, it could be a little nose-wrinkling for others—here are some tips for getting rid of halitosis.