There's more to breathing then meets the nose!
Your sitting in Yoga class and you are told to breath deep through your nose, exhale through your mouth. There are a lot of good reasons for this. Emotionally, deep breathing reduces feelings of stress, aids in achieving a relaxed state, and assists us to put our busy minds to rest by inducing a meditative state, however, one of the most important reasons is purely scientific! According to Dr. Mehmet Oz, it's because of a gas called nitric oxide that's made by your nose and sinus mucous membranes. This gas is produced in small amounts, but when inhaled into the lungs, significantly enhances your lung's capacity to absorb oxygen. Nitric oxide is lethal to bacteria and viruses and is also known to increase oxygen absorption in your lungs from 10-25 percent. This is why it's important to inhale through your nose, especially when you are exercising.
Go ahead, take a deep breath!