Bad breath is most commonly caused by naturally-occurring bacteria on the tongue and in the mouth but, in some cases, it can be linked to systemic diseases as one of the symptoms of a larger condition. A systemic disease is an ailment that affects multiple organs in the body or the body in its entirety. For example, systemic diseases that can cause bad breath include cancer of the mouth or throat, diabetes, or human immunodeficiency virus (HIV). Other systemic conditions known to correlate with halitosis are stomach ulcers, renal failure, metabolic dysfunctions and lung or bronchial infections. Although this list is not exhaustive, and they occur less frequently than mouth bacteria-related bad breath, understanding how these systemic diseases cause bad breath is important in a halitosis diagnosis.

Oral Cavity

80 to 90 percent of bad breath results in the breakdown of bacteria present in the oral cavity. These bacteria feed off of the amino acids present in stagnant saliva, postnasal drip, dead epithelial cells and blood from things like bleeding gums. Often, poor dental hygiene can lead to a buildup of these bacteria called plaque. These plaque buildups are often found in areas such as in faulty dental restorations, unclean dentures, dental abscesses, dental implants, deep cavities and exposed necrotic tooth pulp. This bacteria buildup can inflame tissues and cause gingivitis and periodontitis which can lead to tooth decay and other conditions. In addition to the bacteria causing bad breath by giving off volatile sulfur compounds (VSCs) like dimethyl sulfide, methyl mercaptan, hydrogen sulfide and allyl methyl sulfide, smells due to the emission of indole, skatole and polyamines may also be present. These diseases may increase halitosis levels by adding to the decaying matter and blood in the oral cavity that fuel these bacteria.

Nasal Passages

Systemic diseases in the nasal passage account for five to eight percent of halitosis. This odor can come from problems like nasal infection, sinusitis, airflow inhibitors like polyps, and facial abnormalities like cleft palates. Bad breath from nasal passage diseases has a distinctive cheesy characteristic to its odor.

Tonsils

Tonsils are the tissue that hang in the back of the throat and are the first line of immune defense against pathogens that might travel through the mouth. However, problems with tonsils only account for about three percent of bad breath cases. Tonsilloliths or tonsil stones and tonsil infections can smell foul. Although people often attribute foul breath to tonsils, these do not always cause halitosis.

Diabetes

Diabetes is a systemic disease that can produce very distinctive halitosis if not properly controlled. Although rare in well controlled diabetics, poorly controlled diabetics do not have the insulin to properly use glucose or carbohydrates. Therefore, their bodies produce ketones instead. These ketones add a fruity, acetone odor to the breath.

Cancer

Cancers that are present in the oral cavity, pharynx, tonsils, base of the tongue, larynx or sino-nasal passage can very easily be a contributing factor to halitosis. Squamous cell carcinomas are cancers that form on the surface layer of tissue and cells. The types of cancer likely to cause halitosis are more common in people with high risk factors for sino-nasal and oral cancers such as tobacco or alcohol consumption. To learn more about mouth cancers, visit http://www.cancer.gov/cancertopics/types/oral.

Stomach Ulcers

The most frequent cause of stomach ulcers is a type of bacterium called H. pylori which causes the ulcers by being ingested. Similar to the bacteria that exist in the oral cavity that put out VSCs, this bacterium emits gases and odorous compounds that can travel up the esophageal system and cause bad breath.

Kidney and Liver Failure

Kidneys and livers process and excrete the toxins in the body to help keep people healthy. During kidney or liver failure, toxic metabolites accumulate that are not properly being excreted. These can lead to symptoms of bad breath; a particular type of bad breath associated with liver failure is called fetor hepaticus, or the breath of the dead.

Although bad breath caused by systemic diseases is much rarer than bad breath caused by standard mouth bacteria, it is still important to know about the connections between the two. If halitosis has been diagnosed and standard treatments and improved dental hygiene have been unsuccessful, then a systemic cause, that is a cause that is body-wide or in a completely different area of the body, may be behind the halitosis. As listed above, some of these systemic diseases are very serious conditions and they can have very specific odors that relate to the breath. Therefore, it is very important that a medical professional is notified if a halitosis sufferer suspects that he or she may have a greater underlying systemic disease as the cause of the bad breath.