When each is appropriate
Nasal breathing is the default. Rest, sleep, up to moderate exercise, meditation, and nearly all breathwork practice should be nasal. Mouth breathing is appropriate above threshold exertion, during specific breathwork exhales (4-7-8, physiological sigh), and during acute nasal congestion. Beyond those cases, it is a habit to retrain.
What nasal breathing does
Filters incoming particles. Warms cold air. Humidifies dry air. Adds nitric oxide from the paranasal sinuses, improving oxygen uptake. Slows the breath rate through higher airway resistance. None of these happen through the mouth.
The cost of chronic mouth breathing
No single dramatic effect. A slow accumulation of small costs: no NO delivery, faster breath rate, drier airways, poorer sleep quality, more disturbed circadian breathing patterns. Also common: long-term dental effects from mouth-open sleep.
The retraining path
Auralize\'s Nasal Breathing 101 program is the direct path. Three weeks of gentle paced nasal practice plus daily habit checks. Optional mouth taping for sleep after week two. Do not white-knuckle it — this is a habit shift, not an act of will.