If you are a mouth breather, then your chances of having bad breath are greater. This is because mouth breathing dries out your mouth. When the saliva dries out on surfaces in the mouth, the odor tends to escape. Saliva is also very important for cleansing the mouth, and inhibiting bacterial growth. During the night when the saliva flow is minimal and our mouth is driest, the odor gets worse.

Some people are mouth breathers because their nasal air flow is somehow obstructed. This can also cause odor from you nasal passages.

If you are a frequent mouth breather because of allergies, then some of the nasal discharge may find its way to your tongue, where it can be a major cause of bad breath.