The reason is that your nasal cavities produce the molecule nitric oxide, which chemists abbreviate NO, that increases blood flow through the lungs and boosts oxygen levels in the blood. Breathing in through the nose delivers NO directly into the lungs, where it helps fight coronavirus infection by blocking the replication of the coronavirus in the lungs.The scientist is Distinguished Professor Emeritus of Molecular & Medical Pharmacology, School of Medicine, University of California, Los Angeles. He is one of three pharmacologists who won the Nobel Prize in 1998 for discovering how nitric oxide is produced in the body and how it works. NO protects your blood vessels, which we now know are attacked by the virus.
NO is produced continuously by the 1 trillion cells that form the inner lining, or endothelium, of the 100,000 miles of arteries and veins in our bodies, especially the lungs. Endothelium-derived NO acts to relax the smooth muscle of the arteries to prevent high blood pressure and to promote blood flow to all organs. Another vital role of NO is to prevent blood clots in normal arteries.It also directly attacks the virus.
Other types of cells in the body, including circulating white blood cells and tissue macrophages, produce nitric oxide for antimicrobial purposes. The NO in these cells reacts with other molecules, also produced by the same cells, to form antimicrobial agents to destroy invading microorganisms including bacteria, parasites and viruses. As you can see, NO is quite an amazing molecule.The sinuses in the nasal cavity, but not the mouth, continuously produce NO. This NO is chemically identical to the NO used clinically by inhalation. So by inhaling through the nose, you are delivering NO directly into your lungs, where it increases both airflow and blood flow and keeps microorganisms and virus particles in check.