The nose has a number of very important functions. It prepares the air for the lungs in ways that breathing through the mouth cannot. The nose filters, warms and humidifies the air we breathe. In this way inhaled air is warmed to body temperature, humidified and filtered before it reaches the lungs.
One of the most common presenting symptoms amongst participants in a Buteyko course is a partially or fully blocked nose. It is also one of the earliest symptoms to respond to the breathing exercises. Many people find they can nasal breathe after the first course session, some for the first time in years.
Mouth breathing potentially introduces unfiltered, cold, dry air directly into the lungs. Unfiltered air may carry airborne allergens and dust particles that may irritate and inflame the airways; cold dry air passing over the airway tissue may lead to inflammation, dehydration and greater volumes of thicker tackier mucous. In addition to this, breathing more air than the body requires disrupts the carbon dioxide level in the airways and blood.