<P> Human infants are sometimes considered obligate nasal breathers, but generally speaking healthy humans may breathe through their nose, their mouth, or both . During rest, breathing through the nose is common for most individuals . Breathing through both nose and mouth during exercise is also normal, a behavioral adaptation to increase air intake and hence supply more oxygen to the muscles . Mouth breathing may be called abnormal when an individual breathes through the mouth even during rest . Some sources use the term "mouth breathing habit" but this incorrectly implies that the individual is fully capable of normal nasal breathing, and is breathing through their mouth out of preference . However, in about 85% of cases, mouth breathing represents an involuntary, subconscious adaptation to reduced patency of the nasal airway, and mouth breathing is a requirement simply in order to get enough air . Chronic mouth breathing in children may have implications on dental and facial growth . It also may cause gingivitis (inflamed gums) and halitosis (bad breath), especially upon waking if mouth breathing occurs during sleeping . </P> <P> In the United States, the term "mouth - breather" is sometimes utilized as an insult to imply low intelligence . </P> <P> Mouth breathing has been classified according to etiology into three groups: obstructive, habitual and anatomic . </P> <P> The nasal airway may be compromised partially (where there is increased resistance to the flow of air due to narrowing of the lumen at some point in the upper respiratory tract) or completely obstructed . Such individuals may find it difficult or impossible to breathe through their nose alone . In about 85% of cases, mouth breathing is an adaptation to nasal obstruction . Specific causes of nasal obstruction which have been linked to mouth breathing include antrochoanal polyps . </P>

Where does the term mouth breather come from