The nose is a very complex organ with many important functions.  It prepares the air entering the lungs, filtering out particles, and adjusting the temperature. It also produces a nice even air flow to trigger receptors that help keep the upper airways open; and it plays a key immune function too.

Throughout the day, each nostril takes regular breaks by alternating contraction and expansion called the nasal cycle. This changeover occurs every 2-4 hours. Right now, if you're breathing through your nose, most of the air is going in and out of one side, with a much smaller amount passing through the other.  The opening and closing is done by automatic swelling and deflating of the tissue in your nose. Researchers believe there are two main reasons for this switch-over. First, it fine-tunes our sense of smell. Different scents degrade at different rates depending on their volatility. Some smells are easier to identify in the faster moving airstream in the “open” nostril, while others are better detected in the slower airstream of the “constricted” nostril. And we need all the help we can get – my dog has over 100 million more smell sensors than me!

Second, it keeps the nose in top form. Alternating congestion gives the tiny hairs called cilia that keep a thin mucous film moving in your nose a well-deserved break from filtering while preventing your nostrils drying out. The nose is truly designed for breathing and the mouth for eating and speaking. Make sure you use it.

References

Variation in nasal mucosa congestion during rest