Approximately 50% of people breathe through their mouth.1 This may be due to nasal congestion, enlarged tonsils and adenoids, nasal polyps, enlarged turbinates, deviated septum, perpetual over breathing/hyperventilation, habits, or oral restriction that has led to orofacial myofunctional disorders, etc. Premature birth is also a risk factor. 2
There are unfortunately many negative side effects of oral breathing, which may include the following:
Approximately 10-18% less oxygen is absorbed into the body when mouth breathing occurs versus nose breathing.3 Just think about the effect this may have on structures like your brain and muscles and how one could improve their academic/athletic performance as well as the quality their sleep just by nasal breathing. Additionally, mouth breathing can lead to a chronic habit of hyperventilation and be linked to anxiety, asthma, and many other conditions. See Buteyko Breathing to learn more.
Enlarged Tonsils & Adenoids
It is a common side effect for mouth breathers to develop enlarged tonsils and adenoids. The nose is specifically designed with tiny hairs and mucus to filter air. When oral breathing occurs, the unfiltered air hits the tonsillar tissue directly, making the tissue the first line of defence against bacteria, toxins, air particles, etc. As a result the tonsils and adenoids may become enlarged and inflamed. If the tonsils get very enlarged and make nasal breathing too restrictive, it may lead to a perpetual cycle of mouth breathing.
That said, the enlarged tonsils and adenoids could also be the cause of mouth breathing if the inflammation is coming from another source. In that case, mouth breathing may just be making the inflammation perpetually worse on top of the existing inflammation.
Underdeveloped Arches & Crowded Teeth
There are many factors that control the growth and development of the dental arches such as genetics, the hardness of the foods eaten, oral habits (ex. thumb sucking), etc. But the resting posture of your tongue also plays an incredibly significant role, acting as a natural palate expander during growth and development. The tongue is normally supposed to rest on the palate where it applies pressure to the bone of the palate and may cause bone growth according to the principle of Wolff’s Law.
On the contrary if mouth breathing occurs it allows for a narrowing effect, as the tongue may not counteract the pressure of the cheeks. The palate shape will often form high, vaulted, and narrow as a result. It also tends to grow in a down and back direction, which may result in a gummy smile. This underdevelopment of the jaws often equates to crowded teeth and need for orthodontic treatment.
Elongated Facial Growth
Mouth breathers characteristically develop an elongated narrow face, commonly called long face syndrome. As explained above, the palate may have a narrower development when the tongue posture is low. Therefore, the structures directly above and below (the sinuses and lower jaw) may follow this narrow pattern.
Oral breathers also may present with tired looking eyes for two different reasons. Firstly, from venous pooling, also known as allergic shiners. Secondly, from excess sclera being exposed below the iris, which may result from the drooping/downward growth of the face thus pulling the tissues between the lower eyelid and maxilla. Other commonly seen characteristics are a gummy smile (as previously mentioned), a bump on the nose, little definition of cheekbones, and smaller airway space.
Conversely, nasal breathers typically develop well developed jaws, a wider face, straight teeth, good airway space, straight nose, alert looking eyes, and well-developed cheek bones.
Smaller Airway Space
Here is a study showing the average difference of the airway size in nasal vs. mouth breathing subjects.
To elaborate further on smaller airway space, if the palate is narrow, the nasal cavity above also may be narrow. Another area where there may be restriction is directly behind the tongue. If the jaws are set back, the tongue may have little room in the mouth and as a result may have to take up space in the airway.
If the same volume of air has to pass through a smaller airway, resistance increases which may allow for a more collapsible airway. This is a risk factor for snoring and Obstructive Sleep Apnea (OSA).
Patients also may present with forward head posture in a effort to open the airway more.
Snoring & Obstructive Sleep Apnea (OSA)
Put very simply, snoring is the vibration of structures due to limited air flow, whereas obstructive sleep apnea (OSA) is a partial or full blockage of airflow, commonly caused by the tongue falling against the back of the throat.
To paint a picture for you of what a common apneic event may look like in an OSA patient, lets say that the tongue falls back and blocks the airway. The body would generally try to continue breathing. Movement of the chest or diaphragm may be seen as the respiratory muscles contract. But due to the blockage little to no air can pass through. The person may arouse from sleep, opening the airway and gasping for air. While this blockage occurs the heart rate typically drops, until the person is aroused out of sleep and the heart rate may rapidly increase.
According to American Heart Association, these awakenings, which may occur 5-30x/hr or more, prevent restful sleep and are associated with high blood pressure, stroke, arrhythmia, and heart failure.4
Research shows that obstructive sleep apnea increases the risk of heart failure by 140%, the risk of coronary heart disease by 30%, and the risk of stroke by 60%.5 Heart disease is currently the leading cause of death in the United States.4
There are many ways to treat sleep apnea today, such as continuous positive airway pressure (CPAP) therapy, jaw expansion appliances/orthodontics, mandibular advancement devices, maxillomandibular advancement surgery (MMA), medication, etc. But myofunctional therapy is also shown to be effective, decreasing the apnea-hypopnea index by approximately 50% in adults and 62% in children6, making it a great non-invasive adjunctive treatment. Additionally, with structural changes of the hard tissues with some of the above OSA treatments, myofunctional therapy may serve in preventing relapse.7,8