Halitosis can be subdivided into intra-oral and extra-oral
halitosis, depending on the place where it originates. Most reports now agree that the most frequent sources of
halitosis exist within the oral cavity and include bacterial reservoirs such as the dorsum of the tongue, saliva and
periodontal pockets, where anaerobic bacteria degrade
sulfur-containing
amino acids to produce the foul smelling volatile
sulfur compounds (VSCs), especially
hydrogen sulfide (H(2)S) and methyl
mercaptan (CH(3)SH). Tongue coating is considered to be the most important source of VSCs. Oral malodor can now be treated effectively. Special attention in this overview is given to extra-oral
halitosis. Extra-oral
halitosis can be subdivided into non-blood-borne
halitosis, such as
halitosis from the upper respiratory tract including the nose and from the lower respiratory tract, and blood-borne
halitosis. The majority of patients with extra-oral
halitosis have blood-borne
halitosis. Blood-borne
halitosis is also frequently caused by odorous VSCs, in particular
dimethyl sulfide (CH3SCH3). Extra-oral
halitosis, covering about 5-10% of all cases of
halitosis, might be a manifestation of a serious disease for which treatment is much more complicated than for intra-oral
halitosis. It is therefore of utmost importance to differentiate between intra-oral and extra-oral
halitosis. Differences between intra-oral and extra-oral
halitosis are discussed extensively. The importance of applying odor characterization of various odorants in
halitosis research is also highlighted in this article. The use of the odor index, odor threshold values and simulation of bad breath samples is explained.