Have you ever wondered about the importance of breathing through your nose vs breathing through your mouth? While searching the Internet for an answer to why the cold air seems to freeze up my chest and make breathing very difficult, I stumbled across The Science of Breath. The section on Nostril vs Mouth-breathing had this to say about cold air:
And, moreover, such incorrect breathing admits cold air to the organs, thereby injuring them. Inflammation of the respiratory organs often results from the inhalation of cold air through the mouth.
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Not only do the nostrils serve this important purpose, but they also perform an important function in warming the air inhaled. The long narrow winding nostrils are filled with warm mucous membrane, which coming in contact with the inhaled air warms it so that it can do no damage to the delicate organs of the throat, or to the lungs.
The author says that many diseases can be attributed to the habit of mouth-breathing and says that smallpox, which killed many men-of-war in foreign countries, did not kill a single "nostril-breather"; it only affected those who breathed through their mouths (though I can't help but wonder how he obtained nostril vs mouth-breather data).
I have observed that I breathe through my mouth most the time. Between the ages of thirteen and eighteen I had asthma that was bad enough to make climbing a flight of six stairs difficult. I suppose the habit of mouth-breathing could have formed when I had asthma: Since my lungs needed to get as much air as possible, I subconsciously developed the habit of always breathing through my mouth. (The asthma disappeared when I stopped eating dairy and started exercising.)
What other implications could mouth-breathing have? Of all the organs in our body, the brain uses the most oxygen. What organ is closest to the brain? The nose! Could breathing through our nose somehow provide our brain with a little extra oxygen, thereby increasing its function? When I breathe through my nose, my head automatically feels better; my brain feels clearer and refreshed with every breath. I don't feel any of that when I breathe through my mouth.
I'm going to start doing daily breathing exercises and make a conscious effort to breathe through my nose. The Summary of Techniques and Exercises section of the aforementioned site has some incredible breathing exercises (try a few!).