Halitosis

Halitosis is due to the presence of volatile, disagreeably odorous compounds in the expired air.[1][2][7][8][3] In most cases the odorous compounds are produced by bacteria that accumulate on oral, nasopharyngeal, respiratory, and upper gastrointestinal surfaces.[9][10][11][12] Volatile sulfur compounds (VSCs), diamines, and short-chain fatty acids are usually implicated.[1][2][7][8][3]

It is likely that a complex interaction between several oral bacteria (mainly gram-negative anaerobic flora) leads to production of odorous compounds.[13][14]

Some foodstuffs (e.g., onion, garlic, spiced food, durian fruit), drugs with dimethyl sulfide structures, and, less frequently, some systemic disorders cause odorous agents to circulate in the bloodstream and to be exhaled through alveolar gas exchange into the breath (also known as blood-borne halitosis).[1][2][7][8][3][15][16][17][18]

Systemic diseases include:[15][16]

Acetone-like smell in uncontrolled diabetes mellitus (rare in modern society)
Uremic breath in renal failure
Fetor hepaticus in liver disease
Trimethylaminuria (fish odor syndrome)
Hypermethioninemia.

Physiologic halitosis (morning breath)

This is a mild form of halitosis. It commonly occurs upon waking as a result of increased microbial metabolic activity during sleep, due to a nocturnal reduction in salivary flow and lack of nocturnal physiologic oral cleansing (such as movement of the facial and oral muscles).

Pathologic halitosis due to oral causes

This form of persistent halitosis is due to microbial putrefaction of food debris, cells, saliva, and blood that can occur on the posterior dorsum of the healthy tongue or as a consequence of oral, nasopharyngeal, or respiratory and upper gastrointestinal superficial disease.[1][2][7][8][3] These disorders are better classified as predisposing/risk factors rather than causes.

Pathologic halitosis due to systemic causes

Some systemic diseases cause production and circulation of volatile odorous agents that can be exhaled through alveolar gas exchange into the breath.[2][3][15][16] These include the following:
- Acetone-like smell in uncontrolled diabetes mellitus (rare in modern society)
- Uremic breath in renal failure
- Fetor hepaticus in liver disease
- Trimethylaminuria (fish odor syndrome)
- Hypermethioninemia.
Trimethylaminuria is a rare metabolic disorder caused by excessive blood levels of trimethylamine. This is excreted into body fluids and breath, leading to a persistent oral and body malodor similar to that of rotten fish. The causal factor of excessive free trimethylamine is substrate overload or reduced enzyme (flavin monoxygenase) capacity as a result of an inherited deficiency, drug interaction, liver damage, and/or hormonal modulation.[16]

Halitosis classification

There is no formal classification for halitosis, but it can be considered in 2 different ways.[1][2]

First way to classify halitosis is:

Physiologic halitosis (morning breath, morning halitosis)
Pathologic halitosis due to oral causes or to systemic causes
Pseudohalitosis (including halitophobia).

Second way to classify halitosis is:

Genuine halitosis
- Physiologic halitosis (morning breath)
- Pathologic halitosis due to oral (oral halitosis) or systemic causes (extra-oral halitosis)
Pseudohalitosis.

Pathophysiology

Classification

Halitosis classification