Nose breathing is far superior to mouth breathing. The issue with habitual mouth breathing is that we inhale and exhale too much air (chronic hyperventilation). Hyperventilation leads to an imbalance in the carbon dioxide-oxygen (CO2-O2) exchange. The brain responds by stimulating mucus production to slow our breathing, causing the onset of nasal congestion. This, in turn, creates a vicious cycle that leaves mouth breathers unable to breathe through the nose. Nose breathing slows and optimizes breathing cadence, protecting us from hyperventilation. One of the great functions of the nose is that it acts as a filter for airborne particles in inhaled air. The nose warms and humidifies inhaled air, protecting the lungs in cold or dry environments. And the nose optimizes CO2-02 exchange, which in turn, ensures efficient use of oxygen in the blood.