Halitosis is an abnormal odor emitted from the mouth or other air-filled cavities, such as the nose, sinuses, and throat, and is a more common clinical symptom in the elderly. Determine whether bad breath, can be clarified by sensory analysis, bacterial culture method, chemical analysis, etc. 1, sensory analysis method Sensory analysis method is to evaluate the intensity of bad breath gas using the nose’s sense of smell, is a direct way to determine bad breath, is considered the gold standard for diagnosis. The examinee can communicate and exchange with people around him or her, and the feedback from his or her relatives and friends will be used to evaluate whether or not the breath is bad. The specific method is for the subject to slowly open his or her mouth and breathe at a position about 10 cm from the examiner’s nose, and the examiner will evaluate this odor to clarify whether or not there is an abnormal odor, which is the simplest way to determine bad breath. 2.Bacterial culture method The bacterial culture method refers to the sampling of the oral bacteria of the examined person, through the results of bacterial culture, so as to analyze the nature and number of bacteria in the oral cavity, visually reflect the proportion of the composition of bacteria in the oral cavity, and clarify whether there is bad breath; however, since some oral bacteria cannot grow in the culture medium, the bacterial culture method has limitations for determining whether there is bad breath. 3, chemical analysis method can be used to detect the gas exhaled from the mouth of the person being examined, and can also be used to detect whether there are symptoms of bad breath through the zinc oxide coated film semiconductor sensor.