Here’s what Professor Hallux has to say:
That’s a fantastic question! And like most things about the human body, there’s a really good reason behind it. Lets’ sniff out the answer!
In order to be detected by the brain, smells don’t have to just get up your nose – they have to be absorbed into the mucus in your nasal cavity.
Two nostrils have a bigger surface area than one, so that helps absorb more particles. Also some smells absorb easily, but others take a little longer. Here’s the clever bit. Scientists think that one of your nostrils will tend to sniff more quickly than the other. It’s a bit like having a fast lane and a slow lane!
Smells that are easily absorbed will whizz up the fast lane, but smells that take a bit longer won’t be lost, because they’ll be soaked up on the slow lane.
So having two nostrils helps your brain detect a greater range of smells. And if something is just TOO pongy, pinch your nose. It’s like an instant roadblock!