According to Dr. Richard H. Price, spokesman for the American Dental Association, “Ninety percent of mouth odors come from the mouth itself—either from the food you eat or bacteria that’s already there.”
Mouth odour, or halitosis, is one of the chief reasons people pay a visit to their dentist outside of their regular hygiene appointments. Most innocuously and temporary is after eating certain strongly-flavoured foods like onion or garlic, we experience some odour. Also commonly, food particles left behind after eating, if allowed to remain in the mouth long enough, break down and grow bacteria, which give off an odour. Some people whose teeth are close together tend to be more susceptible to this problem as food between meals is more easily trapped in the teeth and against the gumline.
More seriously, mouth odour can be caused by an accumulation of plaque on the teeth. Plaque on the teeth and at the gumline can lead to gum disease, which left untreated can cause damage to the gums and related bone. One of the primary reasons regular visits to the dentist for a cleaning are recommended is to remove the plaque that if left untreated can lead to larger issues.
Cavities could also be responsible for a bad odour in the mouth; in fact, odour is often an early sign of the presence of a cavity.
Another culprit that causes odour is dry mouth, often caused by either unhealthy salivary glands or certain medications. Saliva contains enzymes and antibacterial compounds that kill the dead cells and remove odour-creating substances.
The other ten percent of persistent mouth odours may be caused by diseases such as respiratory tract infection, diabetes, liver problems, chronic acid reflux, chronic sinus infections and kidney problems.