Although 90 percent of cases of bad breath originate from the mouth, the other 10 percent originate from other sources. Although the nose and sinuses can also be a source of bad breath, blood borne bad breath may be the most common cause outside the mouth. 

Recent findings suggest that a mechanism called blood borne halitosis may account for bad breath that does not originate in your mouth.  The reason for that is that some chemicals present in the blood can be transferred to the air you breathe out and cause a bad smell. 

The sense of smell has evolved to help you detect spoiled food or harmful substances, and it also plays a role in the selection of a romantic partner. 

Bad breath can cause other people to stay away from you, and that has significant consequence, including social anxiety, problems with relationships and productivity, and reduced quality of life.  So all the information that we can bring forward regarding this issue is sure to be helpful to many people. 

These bad smelling chemicals are usually absorbed from the gut and travel to the lungs and enter the air that you breathe out. These chemicals also can come out in your sweat, and urine. 

The most common blood borne bad smelling chemical is dimethyl sulphide. It smells like radish or cabbage. Bacterial species that produce dimethyl sulphide are present in the intestinal tract. If you have elevated levels of dimethyl sulphide in your blood then you have a condition called hyperdimethylsulphidemia . This condition can be caused bacteria in your intestinal tract and also by liver disease or by some other metabolic (whole body) conditions or by medications such as dimethylsulphoxide, cysteamine, and suplatast tosilate. 

Although the dentist is the first practitioner that is seen for bad breath, if bad breath is coming from outside the mouth, then a multi-disciplinary center that has specialists in ENT (ear-nose-throat), periodontology (gum disease) and psychiatry may be the best place to have the the condition properly diagnosed and managed. 

For more info refer to : 

Harvey-Woodworth, C. Dimethylsulphidemia: the significance of dimethyl sulphide in extra-oral, blood borne halitosis. Br Dent J 214, E20 (2013). https://doi.org/10.1038/sj.bdj.2013.329

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