The origin of halitosis comes from the Latin word "halitus" meaning 'breath, exhaled air', and in the Hungarian terminology it means bad and smelly breath. The human body emits a number of volatile molecules, which have a peculiar odour. Their presence is influenced by several factors, such as genetic, nutritional and psychological factors. Since bad breath belongs to taboo subjects, halitosis can often lead to social isolation. To determine the incidence of halitosis, an exact diagnosis is needed which sometimes predestinates the possible treatment as well. Investigators estimate the incidence about 50% in the whole population. The male/female ratio is the same and the incidence is growing with age. The diagnosis can be genuine halitosis, pseudo halitosis and halitophobia. We can divide the genuine type into physiological and pathophysiological subtypes. The cause of the halitosis usually can be found in the oral cavity. The volatile sulfur compounds (VSC) produced by some of the oral bacteria are responsible for its development. Only 10% of the causes are extraoral, mostly inflammation of airways or gastrointestinal disorders. The judgment of halitosis is based on three objective methods: the organoleptic, the sulphide monitoring and the gas cromatography methods. Since the origin of the halitosis is mainly the oral cavity, dentists should treat them. Beyond the dental treatments the enhancement of the oral hygiene, the continuous motivation and monitoring are also very important, such as the use of tongue cleansing and special anti-malodour rinses.