The nose is not simply an alternative route for air to enter the lungs. It is a sophisticated physiological system that filters, humidifies, warms, and chemically processes each breath in ways that mouth breathing cannot replicate. Nasal breathing produces nitric oxide in the paranasal sinuses, a molecule with vasodilatory, antimicrobial, and bronchodilatory properties that is delivered directly to the lungs with each inhale. Mouth breathers forgo this entirely. The consequences extend from sleep quality and oxygen delivery to infection susceptibility and, in children, craniofacial development.
Nitric Oxide and Oxygen Delivery
Nitric oxide produced in the nasal sinuses is inhaled into the lungs with each nasal breath. In the lungs, it acts as a bronchodilator and vasodilator, improving the matching of ventilation to perfusion and increasing oxygen uptake. Studies have shown that nasal breathing increases arterial oxygen saturation compared to mouth breathing at the same respiratory rate. Humming, which resonates the sinuses, increases sinus nitric oxide production by 15-fold and is used as a therapeutic intervention in sinus conditions.
Sleep and Sleep-Disordered Breathing
Mouth breathing during sleep is associated with increased rates of snoring, sleep apnoea, dry mouth, morning headache, and unrefreshing sleep. The Framingham Heart Study data showed that habitual mouth breathing was associated with higher rates of cardiovascular events independent of sleep apnoea diagnosis. Nasal strips, myofunctional therapy, and in some cases mouth taping at night have been studied as interventions to restore nasal breathing during sleep with documented improvements in sleep quality and daytime alertness.
Immune Defence and Airway Filtration
The nasal mucosa contains cilia, mucus-secreting cells, and immunoglobulin A, which together trap and neutralise pathogens, allergens, and particulate matter before they reach the lower airways. The nose also conditions air to near-body temperature and 100 percent humidity before it reaches the bronchi. Mouth breathing delivers unconditioned, unfiltered air directly to the lower airways, increasing local inflammation and susceptibility to respiratory infections. This is particularly relevant for adults with asthma, for whom nasal breathing is a recommended component of management.
- Practise nasal breathing deliberately during low-intensity exercise until it becomes habitual
- Address nasal congestion: allergic rhinitis and septal deviation are treatable and worth treating
- Consider nasal breathing strips at night if you snore or wake unrefreshed
- Humming for 60 seconds in the morning increases sinus nitric oxide production
- If you exercise with an open mouth, reduce intensity until you can breathe nasally: this builds CO2 tolerance over time
Sources
- Lundberg, J.O.N. (2008). Nitric oxide and the paranasal sinuses. Anatomical Record, 291(11), 1479-1484.
- Nestor, J. (2020). Breath: The New Science of a Lost Art. Riverhead Books.
- Fitzpatrick, M.F., et al. (2003). Mouth and nose breathing in obstructive sleep apnoea. European Respiratory Journal, 22(1), 129-133.