The Default Most People Do Not Question
Breathing is so automatic that most people never think about how they are doing it. But there is a meaningful difference between nasal and oral breathing — and the majority of adults, particularly during sleep, breathe through their mouths more than is good for them. Chronic mouth breathing is one of the most common and consistently overlooked contributors to a range of health problems that on the surface appear unrelated.
What the Nose Actually Does
The nose is not simply a passage for air. It filters, humidifies and warms incoming air before it reaches the lungs. It also produces nitric oxide — a molecule with vasodilatory properties that improves oxygen uptake in the lungs and has antimicrobial effects. Nasal passages have turbinates — bony structures covered in mucosa — that create turbulence in the airflow, slowing it down and maximising contact with the mucous membranes that filter pathogens.
When air enters through the mouth, none of these processes happen. The air arrives cooler, drier, unfiltered and without the nitric oxide boost. The respiratory system has to work harder to process it, and the lungs receive oxygen less efficiently.
What Happens During Sleep
Mouth breathing during sleep is strongly associated with snoring and obstructive sleep apnoea. When the mouth is open, the tongue and soft palate are more likely to fall backward, partially obstructing the airway. This creates the conditions for interrupted sleep even in people who do not have diagnosed apnoea — more frequent micro-arousals, reduced time in deep sleep and lower blood oxygen saturation throughout the night.
The downstream effects of this include higher morning blood pressure — several studies have found that habitual mouth breathers have measurably elevated blood pressure compared to nasal breathers matched for age and weight. The mechanism involves the higher sympathetic nervous system activity associated with sleep fragmentation and the absence of the nitric oxide that nasal breathing provides.
The Dental and Structural Effects
Dentists are often the first clinicians to notice mouth breathing. Chronic oral breathing dries out the saliva that normally protects tooth enamel and maintains the pH balance in the mouth, significantly increasing the risk of dental caries and gum disease. The tongue, which in nasal breathers rests against the palate and helps shape the upper jaw, falls lower in mouth breathers — altering the developmental pressures on facial bones over time.
In children this effect is particularly pronounced. Paediatric sleep medicine researchers have documented that children who habitually mouth breathe during the critical years of facial development are significantly more likely to develop narrow upper jaws, crowded teeth and a characteristically elongated lower face — changes that in many cases require orthodontic or surgical correction. The pattern is so consistent that experienced paediatric dentists can often identify chronic mouth breathers from their facial structure alone.
What to Do About It
Myofunctional therapy — exercises that train the muscles of the tongue, lips and face — has a growing evidence base for correcting mouth breathing habits, particularly in children. Nasal strips and dilators can help during sleep by reducing nasal resistance. Addressing the underlying causes of nasal obstruction — allergies, a deviated septum, enlarged adenoids in children — is often the most effective first step. Some people use mouth tape at night, a practice that has attracted attention online and does have some small study support, but which should be approached cautiously and avoided by anyone with sleep apnoea symptoms.
