Q: Is it bad if I breathe mostly through my mouth, not my nose?
A: It can be. It’s okay to breathe through your mouth occasionally—when a bad cold blocks your nasal passages, for example, or when you are exercising strenuously and your muscles need more oxygen. But chronic mouth breathing can dry the mucous lining of the airways.
When done at night, it can cause or worsen dry mouth, especially in older people, which can lead to hoarseness, bad breath, and dental problems. Chronic mouth breathing may also alter airway anatomy, particularly in children, and can worsen sleep apnea.
Moreover, mouth breathing doesn’t warm and moisturize air as efficiently as nose breathing, so the air is more likely to irritate your lungs. And breathing through your nose helps filter out dust and other allergens.
Some people constantly breathe through the mouth because of chronic nasal congestion or an anatomical abnormality in the nose, such as a deviated septum. If you have problems breathing through your nose, consult your doctor, who may refer you to an ear, nose, and throat specialist.
Also see Is Your Tongue Too Big?