Bad breath is not contagious and you cannot catch it from someone else. Also, chronic bad breath (Halitosis) does not come from the stomach. The only stomach odor that someone smells occurs when you burp. Certain foods like garlic and spicy foods once absorbed into the body can release odor through the lungs when you breathe. This food odor is transitory and should not be confused with bad breath. Air flow though the nose of someone with bad breath does not have an offensive odor, only air flow through the mouth. Because our sense of smell has the ability to adjust to odor most people with halitosis are not aware of their bad breath.
Nearly all bad breath originates from the mouth, mostly from the surface of the tongue, below the gum line, between the teeth and other hard to reach areas. The mouth is normally inhabited by bacteria and the balance between the different kinds of bacteria determines the quality of your breath. The odor causing bacteria are anaerobic which means they cannot live in the presence of oxygen. These anaerobic bacteria inhabit the surface of the tongue by residing between the papillae of the tongue which is oxygen deficient i.e. they live "within" the tongue. These bacteria cannot be removed completely with a tongue scraper and will recolonize the mouth following antibody therapy. These naturally occurring bacteria feed on proteins (oral debris) and produce volatile sulfur compounds (VSC) as a by-product of metabolism causing the malodor of bad breath.
Everyone has some level of VSC in their mouth, but it is at a low level that cannot be detected by the nose. When these levels of VSC gets high it becomes detectable as bad breath. Halitosis is rarely associated with certain medical conditions - e.g.: diabetes. If the onset is sudden, grows noticeably worse over a short period of time and is associated with fever, see a doctor.
Q: What causes Bad Breath Odor (Excessive Volatile Sulfur Compounds)?
Anything that decreases the flow of saliva or stimulates the growth of anaerobic bacteria.
Saliva irrigates the mouth, stimulates swallowing thereby flushing away debris. Morning breath occurs due to decreased salivary flow during sleep. As saliva contains oxygen, the dryer your mouth and the thicker your saliva, the less the washing action and the lower the oxygen level creating a more anaerobic environment for bacteria to produce sulfur compounds. This oral stagnation is more pronounced in mouth breathers and those who snore. Alcohol and even certain mouthwashes containing alcohol can dry the oral tissues causing bacteria to profilerate. Certain medications for high blood pressure, antihistamines and depression can decrease saliva flow. Dehydration and stress also reduces the flow of saliva.
These anaerobic bacteria breakdown proteins as the start to digestion, and produce these sulfur compounds as a by-product. These proteins come from oral cellular debris (poor oral hygiene), dead bacteria, saliva, food debris, mucous, post nasal drip and phlegm. Certain conditions cause these bacteria to produce these VSC at an unusually rapid rate. Types of foods may include dairy products especially if you are lactose intolerant and certain foods high in protein. Numerous antibiotics or sulfa-drugs upset the balance of bacterial flora causing some to proliferate and others to perish. An important factor in bacterial growth is the pH of the mouth. Bacteria reproduce faster in a more acid environment. Coffee and acidic foods increase acidity. Hormonal changes have even been implicated with bad breath. During menstruation, estrogen causes sloughing of body lining tissue including that of the mouth. This gives additional nutrition for anaerobic bacteria. Then their is the luck of the draw....your genetics. We all have a different tongue morphology. The more fissured the tongue, the greater the anaerobic environment and the higher the level of VSC.