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(Fetor Oris; Bad Breath; Oral Malodor)


Bernard J. Hennessy

, DDS, Texas A&M University, College of Dentistry

Last full review/revision May 2020| Content last modified May 2020
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Halitosis is a frequent or persistent unpleasant breath odor.

Pathophysiology of Halitosis

Halitosis most often results from fermentation of food particles by anaerobic gram-negative bacteria in the mouth, producing volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan. Causative bacteria may be present in areas of periodontal disease, particularly when ulceration or necrosis is present. The causative organisms reside deep in periodontal pockets around teeth. In patients with healthy periodontal tissue, these bacteria may proliferate on the dorsal posterior tongue.

Factors contributing to the overgrowth of causative bacteria include decreased salivary flow (eg, due to parotid disease, Sjögren syndrome, or use of anticholinergic drugs), salivary stagnation, and increased salivary pH.

Certain foods or spices, after digestion, release the odor of that substance to the lungs; the exhaled odor may be unpleasant to others. For example, the odor of garlic is noted on the breath by others 2 or 3 hours after consumption, long after it is gone from the mouth.

Etiology of Halitosis

About 85% of cases result from oral conditions. A variety of systemic and extraoral conditions account for the remainder (see table Some Causes of Halitosis).

The most common causes overall are the following:

Gastrointestinal disorders rarely cause halitosis because the esophagus is normally collapsed. It is a fallacy that breath odor reflects the state of digestion and bowel function.

Other breath odors

Several systemic diseases produce volatile substances detectable on the breath, although not the particularly foul, pungent odors typically considered halitosis. Diabetic ketoacidosis (DKA) produces a sweet or fruity odor of acetone, liver failure produces a mousy or sometimes faintly sulfurous odor, and renal failure produces an odor of urine or ammonia.


Some Causes of Halitosis


Suggestive Findings

Diagnostic Approach

Oral conditions

Bacteria on dorsum of tongue

Malodorous tongue scrapings, healthy oral tissue

Clinical evaluation

Gingival or periodontal disease

Oral disease, often including bleeding and/or purulent exudate

Apparent during the examination

Often history of poor oral hygiene

Clinical evaluation

Dental consultation

Necrotic oral cancer (rare—usually identified before becoming necrotic)

Lesion usually identifiable during the examination

In older patients, who often have extensive history of using alcohol, tobacco, or both

Biopsy, CT, or MRI

Extraoral disorders

Nasal foreign body*

Usually in children

Purulent or bloody nasal discharge

Visible on examination

Clinical evaluation

Sometimes imaging

Necrotic nasopharyngeal cancer*

Discomfort with swallowing

Clinical evaluation

Necrotic pulmonary infection (eg, lung abscess, bronchiectasis, foreign body)

Productive cough


Chest x-ray

Sputum cultures

Sometimes CT or bronchoscopy

Psychogenic halitosis

Malodor not detected by others

Often history of other hypochondriacal complaints

Clinical evaluation

Sinus infection*

Purulent nasal discharge

Facial pain, headache, or both

Clinical evaluation

Sometimes CT

Undigested food regurgitated when lying down or bending over

Video barium swallow or upper gastrointestinal endoscopy

Ingested substances†

Alcoholic beverages, garlic, onions, tobacco

Use apparent on history

Clinical evaluation

Trial of avoidance

* Malodor is typically more prominent from the nose than the mouth.

† Typically, a diagnosis of exclusion after examination rules out other causes.

Evaluation of Halitosis


History of present illness should ascertain duration and severity of halitosis (including whether other people have noticed or complained), adequacy of the patient’s oral hygiene, and the relationship of halitosis to ingestion of causative foods (see table Some Causes of Halitosis).

Review of systems should seek symptoms of causative disorders, including nasal discharge and face or head pain (sinusitis, nasal foreign body), productive cough and fevers (pulmonary infection), and regurgitation of undigested food when lying down or bending over (Zenker diverticulum). Predisposing factors such as dry mouth, dry eyes, or both (Sjögren syndrome) should be noted.

Past medical history should ask about duration and amount of use of alcohol and tobacco. Drug history should specifically ask about use of drugs that can cause dry mouth (eg, those with anticholinergic effects—see table Some Causes of Xerostomia).

Physical examination

Vital signs are reviewed, particularly for presence of fever.

The nose is examined for discharge and foreign body.

The mouth is examined for signs of periodontal disease, dental infection, and cancer. Signs of apparent dryness are noted (eg, whether the mucosa is dry, sticky, or moist, and whether saliva is foamy, stringy, or normal in appearance).

The pharynx is examined for signs of infection and cancer.

Sniff test

A sniff test of exhaled air is conducted. In general, oral causes of halitosis result in a putrefying, pungent smell, whereas systemic conditions result in a more subtle, abnormal odor. Ideally, for 48 hours before the examination, the patient avoids eating garlic or onions, and for 2 hours before, the patient abstains from eating, chewing, drinking, gargling, rinsing, or smoking. During the test, the patient exhales 10 cm away from the examiner’s nose, first through the mouth and then with the mouth closed. Malodor that is perceived as worse through the mouth suggests an oral etiology; malodor that is perceived as worse through the nose suggests a nasal or sinus etiology. Similar malodor through both nose and mouth may suggest a systemic or pulmonary cause.

If site of origin is unclear, the posterior tongue is scraped with a plastic spoon. After 5 seconds, the spoon is sniffed 5 cm from the examiner’s nose; a bad odor suggests the malodor is caused by bacteria on the tongue.

Red flags

The following findings are of particular concern:

  • Fever

  • Purulent nasal discharge or sputum

  • Visible or palpable oral lesions

Interpretation of findings

Because oral causes are by far the most common, any visible oral disease may be presumed to be the cause of halitosis in patients with no extraoral symptoms or signs, and a dentist should be consulted. When other disorders are involved, clinical findings often suggest a diagnosis (see table Some Causes of Halitosis).

In patients whose symptoms seem to be related to intake of certain food or drink and who have no other findings, a trial of avoidance (followed by a sniff test) may clarify the diagnosis.


Extensive diagnostic evaluation should not be undertaken unless the history and physical examination suggest an underlying disease (see table Some Causes of Halitosis). Portable sulfur monitors, gas chromatography, and chemical tests of tongue scrapings are available but best left to research protocols or to specific dental offices that focus on halitosis evaluation and treatment.

Treatment of Halitosis

  • Regular oral hygiene and dental care

  • Cause treated

Underlying diseases are treated.

If the cause is oral, the patient should see a dentist for professional cleaning and treatment of gingival disease and caries. Home treatment involves enhanced oral hygiene, including thorough flossing, toothbrushing, and brushing of the tongue with the toothbrush or a scraper. Mouthwashes are of limited benefit, but some with oxidant formulations (typically containing chlorine dioxide) have shown greater short-term success. If the patient has a history of alcohol abuse, nonalcoholic mouthwashes should be used. Psychogenic halitosis may require psychiatric consultation.

Geriatrics Essentials

Older patients are more likely to take drugs that cause dry mouth, which leads to difficulties with oral hygiene (as do limited manual dexterity and conditions such as rheumatoid arthritis and Parkinson disease) and hence to halitosis, but they are otherwise not more likely to have halitosis. Also, oral cancers are more common with aging and are more of a concern among older than younger patients.

Key Points

  • Most halitosis results from fermentation of food particles by anaerobic gram-negative bacteria that reside around the teeth and on the dorsum of the tongue.

  • Extraoral disorders may cause halitosis but are often accompanied by suggestive findings.

  • It is a fallacy that breath odor reflects the state of digestion and bowel function.

  • Mouthwashes provide only brief benefit.

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