Halitosis can be caused by oral disease, or by respiratory tract conditions such as sinusitis, tonsillitis, and bronchiectasis, but an estimated 40% of affected individuals have no underlying organic disease.We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments in people with physiological halitosis? We searched: Medline, Embase, The Cochrane Library and other important databases up to July 2008 (BMJ Clinical evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).We found five systematic reviews, RCTs or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.In this systematic review we present information relating to the effectiveness and safety of the following interventions: artificial saliva; cleaning, brushing or scraping the tongue; diet modification; regular or single use of mouthwash; sugar-free chewing gums; and zinc toothpastes.