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Asthma often follows long congestion
No one really knows what causes asthma. The nose is the first line of defense against allergens, viruses, and bacteria. Structures and hairs in it filter the air, and it releases nitric oxide, which kills pathogens on contact. Breathing through the mouth skips all of that.
Respiratory therapists who treat asthmatics over the years see almost all of them show a significant reduction of symptoms when they breathe slowly and through the nose, and a smaller share have no symptoms at all. A few dozen studies show this time and time again. Whether the symptoms come back one day is an open question.
The medications keep many people alive. Decades of oral steroids carry a long list of side effects, from diabetes to autoimmune issues, which is why the question of what caused the asthma in the first place matters.
How does the nose make nitric oxide?
In the 1990s, Swedish researchers led by Jon Lundberg at the Karolinska Institute found that the sinuses release large amounts of nitric oxide into the nose, at levels much higher than in air from the lungs. Nitric oxide slows or kills bacteria, viruses, and fungi, and it widens blood vessels when carried in inhaled air. The gas also acts as a signaling molecule throughout the body. Robert Furchgott, Louis Ignarro, and Ferid Murad received the 1998 Nobel Prize in Physiology or Medicine for discovering its role.
How does the nose filter out particles?
Nasal hairs catch the largest particles, and a sticky layer of mucus traps smaller ones such as pollen and dust. Tiny hair-like structures called cilia beat in waves and sweep the mucus toward the throat, where it is swallowed. This conveyor moves mucus at a few millimeters per minute. Mouth breathing carries air past none of this.
Why does a cold lead to mouth breathing?
Infection triggers inflammation, so blood vessels in the lining of the nose swell and mucus production rises. The passages narrow, and air struggles to get through. The nose accounts for roughly half of the total resistance to airflow in the airways, so even small swelling has a large effect. When it becomes too hard to inhale through the nose, the mouth takes over.
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