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See also: Bad Breath (Halitosis) written for patients

Synonym: bad breath

Halitosis is an unpleasant odour emitted from the mouth.

Breath smells when certain aromatic chemicals are found within it; these include hydrogen sulfide, methyl mercaptan and dimethyl sulfide.

Occasionally, patients may confuse bad breath with bad taste in the mouth.

The most common causes of occasional halitosis include:

  • Smoking cigarettes or cigars.
  • Dry mouth.
  • Drinking alcohol.
  • Artificially induced halitosis - after eating a particularly aromatic meal - eg, garlic, onions, highly spiced food.

Other causes

Crash dieting, or protein-only diets

  • After a few hours the body begins to break down its fat stores and ketones are released. These give the breath a distinctive sweet and sickly smell.

Originating from the mouth

  • Altered blood around the gum can be an important cause and may be found with debris or pus due to gingivitis and periodontal pockets.[1]
  • Acute ulcerative gingivitis is associated with a typical form of halitosis.
  • Acute necrotising ulcerative gingivitis (Vincent's disease, trench mouth) causes the most notable halitosis.
  • Bad morning breath:
    • During sleep the flow of saliva is drastically reduced and the tongue and cheeks move very little. This allows food residues to stagnate in the mouth and dead cells that are normally shed from the surface of the tongue and gums and from the inside of the cheeks to accumulate. As bacteria start to work on them and digest them, an unpleasant smell is generated.
    • Although normal, anyone suffering from nasal congestion who mouth-breathes is more likely to suffer from these actions to a greater extent.
  • Bacteria colonising the tongue and periodontal pockets play an important role in the production of volatile sulfur compounds which can cause halitosis. Regular brushing of the tongue is helpful.[2] Note that plaque on the teeth is not a major cause of halitosis but patients should be advised to exercise careful tooth care.
  • Fixed dentures intensify the development of halitosis, as they make difficult, or even completely impede, the complex of oral cavity hygiene measures.[3]
  • Tonsilloliths (tonsil stones) These are clusters of calcified material that form in the tonsillar crypts, or crevices of the tonsils. They are made up mostly of calcium but can contain other ingredients such as magnesium and phosphorus, and can feel like a small lump in the tonsils. Rarely harmful, they can be a nuisance and hard to remove and can often cause bad breath.[4]

Originating from the nasopharynx

Respiratory tract infections

  • These include, for example, bronchiectasis and other lung infections.

Gastrointestinal disorders

  • Acid reflux - this is commonly believed to be a cause, although there is little evidence. In one postal survey of 160 GPs, 1% of all the proton pump inhibitor prescriptions were for symptoms of halitosis and/or bitter taste (94% response rate).[6]
  • Helicobacter pylori has been found in up to 87% of patients with halitosis, acid taste and burning sensations in the mouth.[7]

Systemic disorders

  • Diabetes, renal or liver disease.

Fish odour syndrome (trimethylaminuria)[8]

  • This is is a rare disorder, characterised by long-standing oral and body malodour.
  • It is caused by an excess of trimethylamine due to a metabolic oxidation defect that produces a pungent ammoniacal odour similar to that of rotten fish.


  • This is another rare metabolic disorder that can lead to oral malodour:[9]


  • This is a condition where people falsely believe they have bad breath.[10]

Often, all these can be excluded and still no cause found.


The following may also cause halitosis:[5]

  • Solvent misuse
  • Betel
  • Chloral hydrate
  • Nitrites and nitrates
  • Dimethyl sulfoxide
  • Disulfiram
  • Some cytotoxic agents
  • Phenothiazines
  • Amfetamines

There are no reliable estimates of prevalence, although several studies report the population prevalence of halitosis (physiological or because of underlying disease) to be about 50%.[11]

The clinical assessment of halitosis is usually subjective and is based on smelling air from the mouth and nose and comparing the two - organoleptic assessment.

  • Odour detectable from the mouth, but not from the nose, is likely to be of oral or pharyngeal origin.
  • Odour from the nose alone is likely to be coming from the nose or sinuses.
  • In rare instances when the odour from the nose and mouth are of similar intensity, a systemic cause of the malodour may be likely.

There is no consensus regarding duration of bad breath for diagnosis of halitosis, although the standard organoleptic test for bad breath involves smelling the breath on at least two or three different days.[11]

  • Investigate and manage possible systemic (non-oral) source if the organoleptic method detects malodour from both the mouth and the nose.
  • Improve oral hygiene by professional and patient-administered tooth cleaning.[1]
  • Regular atraumatic tongue cleaning.[12]
  • Regular use of antimicrobial toothpastes and mouthwashes, such as:
  • Two randomised controlled trials (RCTs) have found that regular use of a mouthwash reduces breath odour at two to four weeks compared with placebo.[14, 15] People in the active treatment group had significantly more tongue discolouration than people using placebo mouthwash after two weeks.
  • Regular dental review to ensure maintenance of effective oral hygiene.
  • Halitophobia (fixated with teeth cleaning and tongue cleaning and frequently using chewing gums, mints, mouthwashes, and sprays in the hope of reducing their distress) warrants referral to clinical psychologist.
  • Eradication of H. pylori in patients with functional dyspepsia and halitosis results in sustained resolution of halitosis during long-term follow-up in the majority of cases.

Did you find this information useful?

Original Author:
Dr Huw Thomas
Current Version:
Dr Roger Henderson
Peer Reviewer:
Dr Helen Huins
Document ID:
2226 (v23)
Last Checked:
14 May 2014
Next Review:
13 May 2019

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.