Many of us have seen a child (or an adult) who appears to be breathing through their mouth. Think of Napoleon Dynamite, the movie character, with his mouth hanging open, blank look in his eyes and long face. What do you think came first, the facial growth or the open mouth?
We all want our children to be beautiful and healthy. Studies show that balanced, beautiful faces with properly functioning muscles ultimately lead to straight teeth. But because children who mouth breathe use different muscles than a nose breather, their faces grow differently. Think again about Napoleon Dynamite and you will see the common features of a mouth breather: long face, open mouth, dry lower lip, long nose. If you delve further you may also see: crowded teeth, shorter upper lip, dull expression, speech issues, changes in posture, difficulties with sleep and large tonsils. Certainly, genetics plays a role in growth, but it is critical to realize that other things influence the way our genes are expressed.
See the figure below for the difference between a nasal and mouth breather.

Photo obtained from Patrick McKeown.
Even worse than the change in the way a face grows, is the health impact of mouth breathing. Faces become narrow and so does the jaw, which leads to crowded teeth. Ear infections are common because of the change in the anatomy of the face. And tonsils are often enlarged because they are being overused to filter bacteria out of the air (a job that is to be done properly by the nose). The nose narrows causing a deviated septum which leads to difficulty with daytime breathing and many times, difficulty with nighttime breathing. Many mouth breathers are diagnosed with sleep disordered breathing.
And this is the real issue: sleep disordered breathing. This may mean different things in different children, but it all has to do with a disruption in sleep. Children may snore, wet their beds, exhibit academic or behavior issues, all because of sleep issues. Those are some of the signs to look for, but if your child is a mouth breather, that should be enough to make you curious. And a recent study by Christian Guilleminault, a prominent researcher in the field of sleep medicine, discussed the need to restore nasal breathing in the treatment of pediatric obstructive sleep apnea. He concluded that “Elimination of oral breathing during wake and sleep may be the only valid ‘finish line’ in pediatric sleep disordered breathing”.
The good news is that if identified early enough, mouth breathers can be converted to nose breathers. Sometimes just awareness is necessary to break the habit. But for patients who suffer from allergies, have enlarged tonsils or have weak muscles, there are breathing exercises like the Buteyko method, or physical therapy called myofunctional therapy, that work to restore nose breathing. The earlier a child is breathing through their nose, the sooner there is a good foundation for facial growth, and ultimately, long term health.