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About 85% of bad breath cases result from oral conditions. A variety of systemic and extra-oral conditions account for the remainder. Bad breath is caused by volatile sulfur compounds or VSCs that are produced by anaerobic bacteria in your mouth.
The first thing that you should do is get a clean bill of health from your dentist. If, after a thorough scaling (oral prophylaxis) procedure, and after eliminating all possible sources of infection and food entrapment in the oral cavity, your halitosis still persists, then we can consider the other less common reasons for bad breath, which i will describe below.
Reflux of stomach acids into the esophagus and as high as the throat is known as gastroesophageal reflux and can cause halitosis ( bad breath). This can be confirmed by tests like barium esophagram, pH monitoring, and endoscopy.
Bad breath or halitosis can be caused by nasal or throat conditions like sinusitis; chronic nasal airway obstruction (such as which might occur with a deviated nasal septum) chronic tonsillitis particularly when associated with deep crevices known as crypts which accumulate partially digested food.
Halitosis may also be be related to odors which are excreted in expired air. Certain drugs release odors into expired breath from the lungs. All of these ingested substances are metabolized usually in the liver with breakdown products traveling in the blood stream where they eventually reach the lung tissues where a gas exchange occurs.
Systemic illnesses can also manifest with bad breath, like ( commonly):
uremia (kidney failure)
I suggest a consultation with a physician to discuss all these causes.
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