Abstract : Halitosis affects more than 60% of the population. In about 8% of the cases, halitosis is related to an ENT pathology, and in less than 1% to gastric dysfunction. Ninety percent of these problems are associated to an oral disease. Gram-bacteria are often responsible of bad breath. They transform some amino-acids in volatile sulphur compounds. These bacteria are, also, directly associated with periodontal diseases which affect a major part of the adult population. These diseases are the most important cause of tooth loss after the age of thirty-five, with progressive destruction of supporting tissues of the teeth