Aetiology

Oral malodour can be due to oral causes or non-oral causes (1).

Oral causes:

• the commonest cause of halitosis is poor oral hygiene –
  • this is due accumulation of food debris and dental bacterial plaque on teeth and the tongue.
  • oral microbes such as Prevotella (Bacteroides) melaninogenica, Treponema denticola, Porphyromonas gingivalis and other gram negative bacteria break down food debris resulting in production of chemicals such as volatile sulphur compounds, diamines, and short chain fatty acids which is responsible for the oral malodour
    
    
• other oral causes include:
  • acute necrotising ulcerative gingivitis (Vincent's disease, trench mouth) – responsible for most notable halitosis
  • acute gingivitis
  • adult and aggressive periodontitis
  • pericoronitis
  • dry socket
  • xerostomia
  • oral ulceration
  • oral malignancy

Non oral causes:

• respiratory disease
  • foreign body
  • sinusitis, tonsillitis
  • lung diseases – malignancy, bronchiectasis, lung abscesses, necrotizing pneumonia (1,2)
• gastrointestinal tract
  • pharyngo-oesophageal diverticulum
  • gastro-oesophageal reflux disease
  • pyloric stenosis or duodenal obstruction
  • Helicobacter pylori infection may cause halitosis
• systemic disease
  • hepatic failure (fetor hepaticus)
  • renal failure (end stage)
  • diabetic ketoacidosis
  • leukaemias
  • Trimethylaminuria (“fish odour syndrome”)
• drugs
  • solvent misuse
  • chloral hydrate
  • nitrites and nitrates
  • dimethyl sulphoxide
  • disulphiram
  • some cytotoxic agents
  • phenothiazines
  • amphetamines

Transient halitosis is common and can be caused by

• volatile foods such as garlic, onions, or spices (durian is reputed to be the worst)
• tobacco and alcohol
• betel nut products (1,2)

Reference:

• (1) Porter S.R, Scully C. Oral malodour (halitosis). BMJ 2006;333(7569):632–635
• (2) ADA Council on Scientific Affairs. Oral malodour. J Am Dent Assoc. 2003;134(2):209-14