The intensity of bad breath may differ during the day, due to eating certain foods (such as garlic, onions, meat, fish, and cheese), smoking, and alcohol consumption. Since the mouth is exposed to less oxygen and is inactive during the night, the odour is usually worse upon awakening ("morning breath"). Bad breath may be transient, often disappearing following eating, drinking, tooth brushing, flossing, or rinsing with specialized mouthwash. Bad breath may also be persistent (chronic bad breath), which affects some 25% of the population in varying degrees. Tongue
The most common location for mouth-related halitosis is the tongue. Tongue bacteria produce malodourous compounds and fatty acids, and account for 80 to 90% of all cases of mouth-related bad breath. Large quantities of naturally occurring bacteria are often found on the posterior dorsum of the tongue, where they are relatively undisturbed by normal activity. This part of the tongue is relatively dry and poorly cleansed, and the convoluted microbial structure of the tongue dorsum provides an ideal habitat for anaerobic bacteria, which flourish under a continually-forming tongue coating of food debris, dead epithelial cells, postnasal drip and overlying bacteria, living and dead. When left on the tongue, the anaerobic respiration of such bacteria can yield either the putrescent smell of indole, skatole, polyamines, or the "rotten egg" smell of volatile sulfur compounds (VSCs) such as hydrogen sulfide, methyl mercaptan, allyl methyl sulfide, and dimethyl sulfide. The presence of halitosis-producing bacteria on the back of the tongue is not to be confused with tongue coating.
Nasal odour may be due to sinus infections or foreign bodies.Halitosis is often stated to be a symptom of chronic rhinosinusitis, however gold standard breath analysis techniques have not been applied. Theoretically, there are several possible mechanisms of both objective and subjective halitosis that may be involved. Tonsils
There is disagreement as to the proportion of halitosis cases which are caused by conditions of the tonsils. Some claim that the tonsils are the most significant cause of halitosis after the mouth. According to one report, approximately 3% of halitosis cases were related to the tonsils. Conditions of the tonsils which may be associated with halitosis include chronic caseous tonsillitis (cheese-like material can be exuded from the tonsillar crypt orifi), tonsillolithiasis (tonsil stones), and less commonly peritonsillar abscess, actinomycosis, fungating malignancies, chondroid choristoma and inflammatory myofibroblastic tumor. Esophagus
The lower esophageal sphincter, which is the valve between the stomach and the esophagus, may not close properly due to a hiatal hernia or GERD, allowing acid to enter the esophagus and gases to escape to the mouth. A Zenkers diverticulum may also result in halitosis due to aging food retained in the esophagus. Stomach
The stomach is considered by most researchers as a very uncommon source of bad breath.