Mouth breathing refers to the habit of breathing through the mouth instead of the nose. Occasional mouth breathing is normal, but chronic mouth breathing can lead to tooth decay, bleeding gums, and gum disease. Mouth breathing can also exacerbate the severity of sleep apnea. 

When people breathe through their mouths, they bypass the nose’s natural filtering, warming, and humidifying functions. Consequently, the air entering the airway is colder, drier, and less filtered. This can lead to increased inflammation of the upper airway and contribute to airway obstruction.

Mouth breathing can also affect the position of the tongue and jaw, and this can lead to further airway obstruction during sleep. A lowered tongue position and lack of support from closed lips may cause the tongue to fall back more easily and partially block a person’s airway.