Nitric oxide

A gas produced in the nasal passages that widens blood vessels and improves airflow and oxygen uptake. Nasal breathing delivers it to the lungs — one reason nasal breathing is emphasized in functional breath training. Most of it is produced in the paranasal sinuses, and humming has been shown to increase the amount released into the nose considerably. Breathing through the mouth largely bypasses this source. The overall health effects of nasal nitric oxide in everyday breathing are still being researched.