Halitosis (chronic bad breath): clinical background, assessment and treatment

Halitosis (chronic bad breath): clinical background, assessment and treatment

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Abstract

Halitosis is a clinical and psychological burden, and many people experience it for shorter or longer periods. How many have persistent bad breath is hard to establish. A meta-analysis of 13 population studies pooled the figures at 31.8 % (95 % CI 24.6-39.0), but the studies used widely differing definitions and measurement methods, and heterogeneity is substantial [2]. The estimate therefore does not describe how many people have clinically verified chronic halitosis. The international Clinical Practice Guidelines on the Diagnosis and Treatment of Halitosis (Shang et al., International Dental Journal, 2026) gather current knowledge into a shared diagnostic framework [1]. The document was written by an international author group and is not a Danish or European society guideline. In most people the cause lies in the mouth. In a minority it lies outside it, in the nose, sinuses, tonsils or lungs, and more rarely in the gastrointestinal tract, metabolism or endocrine system [1]. A gastrointestinal cause should therefore only be investigated when there is an independent clinical suspicion, for example reflux or swallowing difficulties. Where there is, the work-up may include gastroscopy. The odour profile itself can be characterised with gas analysis for bad breath at EndoCap.

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1. Classification

The international consensus divides halitosis into three categories:

I. Genuine halitosis - persistent malodour that can be confirmed by someone other than the patient, usually by clinical organoleptic assessment and sometimes supported by instrumental measurement. There is no universal instrumental threshold that on its own decides whether halitosis is present.

• Physiological halitosis: transient odour, e.g. "morning breath" from reduced salivary flow during sleep, or short-term food-induced odour (garlic, onions, spices).
• Pathological halitosis:
  • Intraoral: rooted in the oral cavity, and by far the largest group [1].
  • Extraoral: a minority. The source may be the nose, sinuses, tonsils or lungs, and more rarely the gastrointestinal tract, metabolism or endocrine system [1].

II. Pseudohalitosis - the patient experiences persistent bad breath, but no corresponding finding emerges on clinical assessment. Many feel better after a dental review and an explanation of the results, but not everyone does, and the experience can persist [1].

III. Halitophobia - a persistent belief in bad breath that does not change with examination or treatment and takes up a great deal of daily life. This needs an assessment in its own right, and psychological or psychiatric evaluation may be relevant [1]. Neither a negative gas measurement nor a single organoleptic assessment can on its own rule out a physical cause or establish a psychiatric diagnosis.

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2. Aetiology: where the odour comes from

The odour itself usually arises from volatile sulfur compounds (VSCs): hydrogen sulfide (H₂S), methyl mercaptan (CH₃SH) and dimethyl sulfide ((CH₃)₂S).

• Tongue coating: the posterior third of the tongue dorsum is an important reservoir. Anaerobes degrade sulfur-containing amino acids (cysteine, methionine) into sulfur compounds [1].
• Periodontal disease: periodontitis harbours a subgingival anaerobic reservoir where sulfur compounds can be produced [1].
• Systemic conditions: a few serious conditions, including severe diabetic ketoacidosis, advanced liver disease and renal failure, can be accompanied by a characteristic breath odour. Odour is not a diagnostic test. Such conditions are identified through symptoms, examination and blood tests, not through the smell of the breath [1].

Other factors do not generate sulfur compounds themselves but can create conditions in which bacteria thrive:

• Conditions of the oesophagus and stomach: the consensus document lists reflux, Zenker's diverticulum, inflammatory bowel disease and Helicobacter pylori among extraoral causes, which together account for a small share of cases [1]. The mechanism is not established, and the link should only be pursued when there are independent gastrointestinal symptoms. See also GERD, swallowing difficulties and Barrett's oesophagus.
• Anatomical traps: necrotic pulp, open root canals, ill-fitting prostheses and tonsilloliths protect debris and bacteria from salivary clearance.
• Reduced saliva and dry mouth: saliva contains antimicrobial enzymes and mechanically clears debris. Hyposalivation means objectively reduced salivary flow, whereas xerostomia is the subjective feeling of a dry mouth; the two do not always go together. Sjögren's syndrome, mouth breathing and many medicines reduce salivary flow and thereby clearance [1].

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3. Assessment

The complaint should be assessed clinically before treatment [1]:

1. Organoleptic assessment - the central clinical method. A trained clinician smells the exhaled breath and scores odour intensity. The method is subjective and examiner-dependent, but it is inexpensive, direct and used as the clinical reference method [1]. How to prepare is agreed with the clinic; protocols differ between centres.
2. Gas chromatography (GC) - an adjunct. Separates and quantifies the individual sulfur compounds and is used mainly at specialist centres and in research [1]. A gas measurement cannot by itself decide whether the source is inside or outside the mouth.
3. Electrochemical VSC monitors (e.g. Halimeter). Portable measurement of total sulfur compounds - can be used to follow a course over time, but it cannot resolve the individual gases [1].

No single method can determine the cause on its own. The assessment rests on examination of the mouth, the history and the other findings.

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4. Treatment - matched to the verified cause

Mechanical cleaning is the foundation

• Cleaning the posterior tongue dorsum is part of daily oral hygiene and can lower sulfur compound levels [1]. How often, and with what, is agreed with a dentist or dental hygienist.
• Professional periodontal therapy (scaling and root planing) clears the subgingival anaerobic reservoir in patients with gum disease.

Chemical agents are a selective add-on

• Mouth rinses: chlorhexidine, cetylpyridinium chloride and zinc can be used selectively, and usually for short periods, alongside mechanical cleaning when the dentist judges there is reason to. Chlorhexidine can stain teeth and cause transient taste disturbance and is not a universal first choice [1]. These agents do not replace treating the underlying cause.
• Oral probiotics: lozenges containing Streptococcus salivarius K12 or M18 are mentioned in the consensus document, but part of the cited basis is laboratory (in vitro) work, and the clinical studies are small and short. They are not standard treatment, and there is no evidence that they prevent recurrence [1].

Interdisciplinary referral

• A dental assessment first of teeth, gums, tongue and dentures. That is where the cause lies in the large majority [1].
• Suspected source in the nose, sinuses or tonsils → ENT.
• Independent gastrointestinal symptoms such as reflux, swallowing difficulty or abdominal pain → medical assessment, which may include gastroscopy. Bad breath alone is not an indication for gastroscopy.
• In pseudohalitosis, going through the findings helps some people but not all, and the experience should be taken seriously. Halitophobia needs an assessment in its own right, in which psychological or psychiatric help may play a part, and repeated dental procedures without findings are rarely the way forward [1].

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Work-up at Kirurgen.dk

Halitosis is assessed and treated primarily by dental professionals. If there are also independent symptoms from the oesophagus or stomach, we offer oral gastroscopy, nasal gastroscopy and work-up of GERD and swallowing difficulties. See also the gut-brain axis and gut microbiome and probiotics.

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References

1. Shang J, et al. Clinical Practice Guidelines on the Diagnosis and Treatment of Halitosis. Int Dent J. 2026;76(2):109436. Published online 11 February 2026. International consensus document from an international author group, not a Danish or European society guideline. PubMed · PMC12914797 · DOI 10.1016/j.identj.2026.109436
2. Silva MF, Leite FRM, Ferreira LB, et al. Estimated prevalence of halitosis: a systematic review and meta-regression analysis. Clin Oral Investig 2018;22(1):47-55. PubMed