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Bad Breath



Bernard J. Hennessy

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

Last full review/revision Jun 2020| Content last modified Jun 2020

Bad breath is a frequent or persistent unpleasant odor to the breath.

Other breath odors

Certain diseases produce substances that are detectable on the breath, but these odors are typically mild and not considered bad breath. For example,

  • Liver failure gives the breath a mousy or sometimes faintly rotten egg-like (sulfurous) odor.
  • Kidney failure makes the breath smell like urine or ammonia.
  • Severe, uncontrolled diabetes makes the breath smell like nail polish remover (acetone). 

Causes of Bad Breath

Most bad breath is caused by problems in the mouth. Causes that contribute to bad breath are listed in table Some Causes and Features of Bad Breath.

Common causes

The most common causes of bad breath are

  • Periodontal diseases
  • Odor-causing bacteria on the tongue
  • Certain foods and alcoholic beverages
  • Tobacco use

Bad breath is most often caused by the action of certain mouth bacteria on food particles in the mouth. These bacteria break down (ferment) the food particles into foul-smelling substances. These bacteria are more common among people with periodontal diseases (such as gingivitis and periodontitis) and poor oral hygiene.

Periodontal diseases inflame and destroy the structures surrounding and supporting the teeth, such as the gums and the outer layer of the tooth root, and are caused mainly by an accumulation of certain bacteria. These bacteria grow in deep pockets that surround the teeth. Such bacteria can also grow on the back of the tongue, even in people who do not have periodontal disease. These bacteria can also overgrow due to a decrease in the flow of saliva (caused by some diseases or the use of certain drugs—see Dry Mouth) or a decrease in the acidity of saliva.

After digestion, odors caused by certain foods or spices, such as onions or garlic, pass from the bloodstream into the lungs. The odors are then exhaled and may be unpleasant to others. For example, the odor of garlic can be smelled on the breath by others 2 or 3 hours after it is eaten, long after it is gone from the mouth and stomach. Oral hygiene cannot remove these odors.

Bad breath is more common among smokers than nonsmokers.

Less common causes

Less common causes of bad breath include

Although people commonly think that gastrointestinal disorders cause bad breath, they rarely do because the muscular channel that connects the throat with the stomach (esophagus) is normally collapsed. Bad breath is not caused by poor digestion, nor does it indicate how a person’s digestive system or bowels are functioning. However, rarely, a pouch in the esophagus (Zenker diverticulum), present at birth in some people, can collect food particles. The food particles can decompose and create a foul odor.

Bad breath that is imagined is called psychogenic halitosis (pseudo-halitosis). People believe that their breath smells bad when it actually does not. This problem may occur in people who tend to exaggerate normal body sensations or in people who have a serious mental disorder, such as schizophrenia. Some people with obsessive thoughts have an overwhelming sense of feeling dirty and believe that their breath smells bad.

Some Causes and Features of Bad Breath


Common Features*


Disorders in the mouth (oral)

Bacteria on the back of the tongue

Unpleasant-smelling tongue scrapings

Healthy gums and teeth

A doctor’s or dentist's examination

Periodontal disorders, such as gingivitis and periodontitis 

Affected gums and teeth noted during the examination

In people with a history of poor oral hygiene

A dentist’s examination

Cancers of the mouth (most are identified during a doctor's or dentist's examination long before they cause bad odors)

Usually identified during the examination

More common among older people, who often have an extensive history of using alcohol and/or tobacco

Biopsy, CT, or MRI

Disorders outside the mouth (extraoral)

A foreign object (body) in the nose†

Often a pus-filled or bloody discharge from the nose

Seen during the examination

Usually in children

A doctor's examination

Sometimes imaging

Cancer of the nasal passages and upper throat†

Discomfort when swallowing

A doctor's examination

Lung infections, such as a lung abscess, bronchiectasis, or an infection caused by an inhaled foreign object

Cough that produces blood or sputum (phlegm)


Chest x-ray

Cultures of sputum

Sometimes CT or bronchoscopy

Imagined halitosis (psychogenic halitosis)

Unpleasant smell not detected by others

Often in people known to exaggerate other normal body sensations

A doctor's examination

Sometimes a consultation with a psychologist

Sinus infection†

A pus-filled discharge from the nose

Face pain, headache, or both

A doctor's examination

Sometimes CT

Zenker diverticulum

Gastroesophageal reflux disease

Spitting up of undigested food (regurgitation) when lying down or bending over

Video of the upper digestive tract after barium is given by mouth (barium swallow)

Swallowed or inhaled substances

Alcoholic beverages, garlic, onions, tobacco

Apparent based on the person's history

Diagnosed after the doctor's examination rules out other causes

A doctor's examination

Avoidance of the substance to see if symptoms go away

* Features include symptoms and the results of a doctor's or dentist's examination. Features mentioned are typical but not always present.

† The odor is typically more noticeable from the nose than from the mouth.

CT = computed tomography; MRI = magnetic resonance imaging.

Evaluation of Bad Breath

Bad breath rarely requires an immediate evaluation by a doctor or dentist. The following information can help people decide whether an evaluation is needed and help them know what to expect during the evaluation.

Warning signs

Certain symptoms and characteristics are cause for concern. They include

  • Fever
  • Pus-filled (purulent) sputum or discharge from the nose
  • Visible or touchable abnormal spots in the mouth

When to see a doctor

People who have fever or purulent sputum or nasal discharge or who may have inhaled a foreign object should see a doctor right away. People who discover an abnormal spot in their mouth should see a dentist within several days.

People with bad breath but no warning signs and who otherwise feel well should see a dentist when they are able.

What the doctor does

Dentists and doctors first ask questions about the person's symptoms and medical history. They then do a physical examination. What they find during the history and physical examination often suggests a cause of the bad breath and the tests that may need to be done (see table Some Causes and Features of Bad Breath).

The sniff test is a helpful part of the examination that can help tell whether the bad odor is coming from a nose or sinus disorder versus a mouth or lung disorder. The person exhales about 4 inches (about 10 centimeters) away from the doctor’s nose, first through the mouth with the nose pinched shut and then through the nose with the mouth closed. If the odor is worse through the mouth, the cause most likely originates in the mouth. If the odor is worse through the nose, the cause most likely originates in the nose or sinuses. If the odor is similar from both the nose and the mouth, the cause most likely originates from another part of the body or the lungs. If the examiner is unable to tell where the cause originates, the back of the tongue is scraped with a plastic spoon. After 5 seconds, the spoon is sniffed. A bad odor on the spoon shows that the likely problem is bacteria on the tongue.


The need for testing depends on what the doctor finds during the history and physical examination, particularly whether warning signs are present. Some specialists who focus on bad breath have unusual testing equipment, such as portable sulfur monitors, gas chromatography, and chemical tests for tongue scrapings. Such testing is rarely needed except for medical research.

The doctor may suggest that people whose symptoms seem to be related to ingested or inhaled substances avoid the suspected substances for a period of time to see whether the symptoms go away (trial of avoidance).

Treatment of Bad Breath

  • Treatment of the cause
  • Regular oral hygiene and dental care

Once diagnosed, any causes of bad breath are treated.

Physical causes can be removed or corrected. For example, people can stop eating garlic, onions, and other odor-producing food and stop smoking. If the cause is oral, people should see a dentist for professional cleaning and treatment of periodontal diseases and cavities. At home, people should improve their daily oral hygiene routine, including thorough flossing, toothbrushing, and brushing the top and back of the tongue with the toothbrush or a tongue scraper. Many deodorant mouthwashes and sprays are available, but these are of limited benefit. The effects of most of these products do not last more than 20 minutes. People recovering from alcohol use disorder should use alcohol-free mouthwashes.

People with psychogenic halitosis may need to have a psychiatric evaluation.

Essentials for Older People

Older people are more likely to take drugs that cause dry mouth, which leads to difficulties with oral hygiene and hence to bad breath. Oral cancers, another cause of bad breath, also are more common with aging. Older people are otherwise not more likely to have halitosis.

Key Points about Bad Breath

  • Most bad breath is caused by fermentation of food particles by bacteria in the mouth.
  • Disorders outside the mouth may cause bad breath but are often recognizable based on findings during a doctor's or dentist's examination.
  • Bad breath is not caused by poor digestion, nor does it indicate how a person's digestive system or bowels are functioning.
  • The effects of mouthwashes do not last very long.

More Information about Bad Breath


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