Halitosis is a condition of oral health which may be an indicator of serious diseases. It is caused by the presence of sulphured compounds, such as H2S, inside patient's mouth. Traditionally, bad breath analysis has been carried out by equipment based on gases chromatography. Nowadays, sensors and equipment based on electrochemical measurements have been also proposed. In this paper, an optical halimeter based on measurements of reflectance changes is proposed. Optical components and the chemical sensor have been included in a flow cell. Experimental tests show that it is possible to measure H2S optically.