Why do we have two nostrils?

There – I have raised another weird question. But my question is not completely irrational. I mean seriously, think about it.
Our faces have a lot of holes. We have two ears and two eyes, it makes sense because the difference in time it takes for sound to reach one ear and the other allows us to localise where the sound is coming from. And having two eyes gives us two slightly different perspectives that we can put together in order to perceive depth.

But why do we have two nostrils? I mean our sense of smell isn’t good enough to localise one nostril over the other. Why not just have a big hole in our nose like we have a mouth?

Well, Stanford University’s Olfactory Research Project investigated this and they found that throughout the day, one nostril inhales air better and faster, now which one is dominant changes throughout the day but having a good air sucking nostril and a not so good air sucking nostril is important. We need both, because you see odorants and molecules are absorbed by our skin and snot by different rates. Some things are absorbed so quickly that they need to be rushed on to the olfactory before they’re absorbed earlier on in the nose.
Other molecules, other odorants are slowly absorbed and they need to be given time to get to the receptors, not just rushed right to the lungs. So having two nostrils allows us to smell more things. Alright… so let’s smell weird stuff.

How does out space smell like? Uh, okay, right… it’s a tough question and it actually doesn’t make much sense because space is a near vacuum. If you went into space and took your helmet off to smell it, well, all of the air in your lungs, throat and nose will be violently sucked right out. Wait, I just got off topic.

Coming back to the topic, seemingly not, we only breathe through one nostril at a time (try it yourself). At the time of writing this article, my left nostril is doing more hard work although “righty” will soon take over, as the human “nasal cyclecauses my nostrils to swap jobs every few hours.

Why does this happen?

During the nasal cycle, one nostril experiences a swelling as blood vessels engorge, allowing less air to flow through the shrunken nasal cavity. The swelling is caused by erectile tissue, identical to found “down under,” if you know what I mean. So, does taking a Viagra tablet worsen one’s sense of smell? That’s a question yet to be answered. (I appreciate that if you’ve just taken a Viagra tablet, going around smelling things is probably the last thing on your mind).

Even though it appears that only one nostril is doing its job at any one time, it is widely believed (but not proven) that both nostrils are actually working on different smells to provide us with the ability to recognise a broad spectrum of stinks.

Smells come in two forms: odour chemicals that dissolve quickly in mucus, and those that dissolve slowly (as I also mentioned earlier). By breathing in air at different rates through our different nostrils, we are providing the chemicals with varying amounts of time to dissolve in the snot before being detected by the olfactory cells. The “unblocked” nostrils deals with the fast dissolving chemicals while the swollen, seemingly redundant nostril hands the slow dissolving odours.

References & Resources

  1. Image via Peaceful Pawsibilities.
  2. Kathleen O’Toole. (1999). Stanford University Olfactory Research Project: Smelling roses: Your nostrils may part ways. Retrieved from: http://news.stanford.edu/news/1999/november10/smell-1110.html
  3. Esther Inglis-Arkell. (2012). io9: Why we evolved two nostrils (hint: it’s all about domination). Retrieved from:
    http://io9.com/5880616/why-we-evolved-two-nostrils-hint-its-all-about-domination
  4. Gavin Hammond. Null Hypothesis: Useless Bits of Body. Retrieved from:
    http://www.null-hypothesis.co.uk/article/922
  5. Michael Stevens. (2012) Vsauce: Why Do We Have Two Nostrils? Retrieved from:
    http://youtu.be/eiAx2kqmUpQ
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10 comments

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