The most common location for (mouth-related) halitosis is the tongue. Tongue bacteria produce malodourous compounds and account for 80 to 90% of all cases of mouth-related bad breath. Large amounts of naturally occurring bacteria are often found at the back of the tongue, where they remain relatively undisturbed by normal activity. This part of the tongue is relatively dry and poorly cleansed, and bacterial populations can thrive on remnants of food deposits, dead epithelial cells, and postnasal drip.
Cleaning your tongue
The most common reason to clean your tongue is for the control of bad breath. Methods used against bad breath, such as mints, mouth sprays, mouthwash or chewing gum, may only temporarily mask the smells created by the bacteria on your tongue, but cannot cure bad breath because they don’t actually remove the source of the bad breath. In order to prevent the production of malodourous compounds, the bacteria on the tongue must actually be physically removed, as must the decaying food debris present on the rear areas of the tongue. Most people who clean their tongue use a tongue cleaner (tongue scraper), or a toothbrush. Specially designed tongue cleaners are a lot more effective (collecting and removing the bacterial coating) than toothbrushes (which merely spread the bacterial accumulations on the tongue and in the mouth).
The average mouth contains over 600 types of bacteria. Several dozen of these can produce high levels of bad smells when incubated in the laboratory. Other parts of the mouth may also contribute to the overall smell, but are not as common as the back of the tongue.
There is some controversy over the role of periodontal diseases in causing bad breath. Whereas bacteria growing below the gumline (subgingival dental plaque) have a foul smell upon removal, several studies reported no statistical correlation between malodor and periodontal parameters.
The second major source of bad breath is the nose. In this occurrence, the air exiting the nostrils has a pungent odour that differs from the oral odour. Nasal odour may be due to sinus infections or foreign bodies.
In general, putrefaction from the tonsils is considered a minor cause of bad breath, contributing to some 3–5% of cases. Approximately 7% of the population suffer from small bits of calcified matter in tonsillar crypts called tonsilloliths that smell extremely foul when released and may cause bad breath.
The Cardia, which is the valve between the stomach and the oesophagus, may not close properly due to a Hiatus Hernia, allowing acid to enter the oesophagus and gases escape to the mouth. A Zenker’s diverticulum may also result in halitosis due to aging food retained in the esophagus.
The stomach is considered by most researchers as a very rare source of bad breath.
There are a few systemic (non-oral) medical conditions that may cause bad breath, but these are extremely infrequent in the general population.