Background Since most oral malodor originates from microbial activities in the mouth, the role of microorganisms in producing malodorous gases has been clarified by numerous studies, accompanied by the development of analytical techniques for treatment of halitosis. Highlight Oral microorganisms should be controlled to prevent aspiration pneumonia, especially for elderly perioperative patients. Malodorous gases from the mouth can be an indicator of oral or systemic conditions among patients in intensive care units. Recently, malodorous gases originating from oral microorganisms have been reported as a causal factor in carcinogenesis. Conclusion Further analysis of oral malodor might be useful in accessing the risk of aspiration pneumonia and oral cancer.
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