In most cases (85--90%), bad breath originates in the mouth itself. The intensity of bad breath differs during the day, due to eating certain foods (such as garlic, onions, meat, fish, and cheese), obesity, smoking, and alcohol consumption. Since the mouth is exposed to less oxygen and is inactive during the night, the odor is usually worse upon awakening ("morning breath"). Bad breath may be transient, often disappearing following eating, brushing one's teeth, flossing, or rinsing with specialized mouthwash.
Bad breath may also be persistent (chronic bad breath), which is a more serious condition, affecting some 25% of the population in varying degrees.
Contrary to the popular legend that Listerine coined the term halitosis, it actually dates from the 1870s, although it became commonplace in the 1920s when a marketing campaign promoted Listerine as a solution for "chronic halitosis". Halitosis combines the Latin halitus, meaning 'breath', with the Greek suffix osis often used to describe a medical condition, e.g., "cirrhosis of the liver". Bad breath is not, however, a modern affliction. Records mentioning bad breath have been discovered dating to 1550 B.C. A mouthwash of wine and herbs was one recommended way of solving the problem. Cause Tongue
The most common location for mouth related halitosis is the tongue. Tongue bacteria produce malodorous 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. Cleaning the tongue
The most widely-known reason to clean the tongue is for the control of bad breath. Methods used against bad breath, such as mints, mouth sprays, mouthwash or gum, may only temporarily mask the odors created by the bacteria on the tongue, but cannot cure bad breath because they do not remove the source of the bad breath. In order to prevent the production of the sulfur-containing compounds mentioned above, the bacteria on the tongue must be removed, as must the decaying food debris present on the rear areas of the tongue. Most people who clean their tongue use a tongue cleaner (tongue scraper), or a toothbrush.