Abstract: Halitosis is defined as an unpleasant odour from the oral cavity, and it has become one of the causes that influence sociality and mental health, 90% of which is intra-oral halitosis, and the main odour-forming gases of which are hydrogen sulfide and methyl mercaptan. The lack of balance between the micro-ecology in the oral cavity causes the prevalence of anaerobes, which is currently considered to be blamed for the intra-oral halitosis. In this paper, the microorganisms related to the intra-oral halitosis and the generation mechanism of volatile sulfur compounds (VSC) are summarized, in order to clarify its pathogenesis. Existing research has revealed that various microorganisms in the oral cavity, including periodontal pathogens, S. moorei, streptococcus salivarius，Candida and some other anaerobes are closely associated with the occurrence of halitosis. Deglycosylation of glycoproteins and the degradation of sulfur containing proteins play an important role in the generation mechanism of VSC including hydrogen sulfide and methyl mercaptan. Bacteria plays an important part in these two steps. β-galactosidase of G+ bacteria plays a main role in deglycosylation of glycoproteins. L-cysteine desulfurase of G- bacteria can degrade cysteine into hydrogen sulfide and METase of G- bacteria can degrade methionine into methyl mercaptan. The aim of this review is to provide some ideas for the etiological analysis, diagnosis and treatment of halitosis in the future.

Key words: Intra-oral halitosis, Microorganisms, Volatile sulfur compounds, Generation mechanism, Glycoproteins