Everyone has bad breath sometimes, and some people have chronic bad breath all the time, 25 to 50 percent, depending on the population. Morning bad breath is due to overnight dryness when salvia flow is at it lowest, enhancing the growth of oral bacteria. Bacteria biofilm accumulates on and around the teeth, and is also part of tongue coating, especially on the dorusm of the tongue. Eating and drinking in the morning tends to eliminate overnight bad breath, but sometimes it is a chronic problem.
Ninety percent of bad breath can be attributed to oral causes including caries, periodontal disease, poor oral hygiene, and tongue coating. The gold standard measures of measuring bad breath is organolepic testing or smelling the person's breath. It is also measured by the level of unpleasant smelling volitale sulfur compounds (VSC) in the mouth and air.
Researchers at three universities in The Netherlands reviewed research to determine if tongue cleaning with a scraper or toothbrush in addition to regular oral hygiene would reduce oral malodor. Of the 405 studies and abstract their search produced, 22 full text articles were read and 17 of these were excluded as they didn't established criteria they were looking for in the studies The five studies that did fit all criteria were evaluated and compared, showing that tongue scraping or brushing does reduce oral malodor. The studies did not evaluate chronic bad breath.