Halitosis is a symptom and not a diagnosis. Rather, the topic represents a spectrum of disorders, including intra-oral, otorhinolaryngological, metabolic, systemic, pulmonary, psychological and neurological conditions. Halitosis may be the third most common trigger for patients to seek dental care and can cause significant impact on patient quality of life. About 10% of all genuine halitosis cases are attributed to extra-oral processes. Some authorities have reported that the nasal cavity and the oropharynx are the most common sites of origin of extra-oral halitosis. However, recent evidence appears to suggest that blood borne halitosis may be the most common subtype of extra-oral halitosis. Tangerman and Winkel report that dimethyl sulphide was the main volatile implicated in extra-oral blood borne halitosis. They proposed a hitherto unknown metabolic condition by way of explanation for this finding, resulting in systemic presence of dimethyl sulphide in blood and alveolar breath. This paper reviews the knowledge base regarding the behaviour of dimethyl sulphide in physiological systems and those disorders in which blood borne halitosis secondary to dimethylsulphidemia is thought to have an aetiopathological role.