Halitosis (bad breath) is caused by a number of volatiles originating, in most cases, in the oral cavity (intra-oral halitosis). These unpleasant smelling gases are volatile sulphur compounds such as hydrogen sulphide, methyl mercaptan and dimethyl sulphide secreted as a result of bacterial metabolism. Bacteria on the tongue dorsum, as well as oral pathologies such as gingivitis and periodontitis, are the main causes of intra-oral halitosis. Saliva has a number of functions that can affect intra-oral halitosis, such as mechanical cleaning, moistening of the oral cavity and antibacterial properties. Very low secretion of saliva (hyposalivation) can affect intra-oral halitosis.