Halitosis or bad breath occurs when noticeably unpleasant odors are exhaled in breathing. Halitosis is estimated to be the third most frequent reason for seeking dental aid, following tooth decay and periodontal disease.
In most cases (85–90%), bad breath originates in the mouth itself. The intensity of bad breath differs during the day, due to eating certain foods (such as garlic, onions, meat, fish, and cheese), obesity,[medical citation needed] smoking, and alcohol consumption. Since the mouth is exposed to less oxygen and is inactive during the night, the odor is usually worse upon awakening ("morning breath"). Bad breath may be transient, often disappearing following eating, brushing one's teeth, flossing, or rinsing with specialized mouthwash.
Bad breath may also be persistent (chronic bad breath), which is a more serious condition, affecting some 25% of the population in varying degrees.
Contrary to the popular legend that Listerine coined the term halitosis, it actually dates from the 1870s, although it became commonplace in the 1920s when a marketing campaign promoted Listerine as a solution for "chronic halitosis". Halitosis combines the Latin halitus, meaning 'breath', with the Greek suffix osis often used to describe a medical condition, e.g., "cirrhosis of the liver". Bad breath is not, however, a modern affliction. Records mentioning bad breath have been discovered dating to 1550 B.C. A mouthwash of wine and herbs was once recommended way of solving the problem.
Halitosis has been classified by location of the cause of the malodor and by aetiology. The primary subdivision is between Genuine halitosis and pseudo halitosis.
Where halitosis is genuine, this can be subdivided according location, for example intra-oral halitosis (within the mouth) and extra-oral halitosis (outside the mouth). Intraoral halitosis is also known as oral malodor and accounts for some 80-90% of genuine halitosis cases.
Genuine halitosis can also be thought of as either physiological, or pathological.
- Genuine Halitosis
- oral malodor (intra-oral halitosis)
- Extraoral halitosis
- Extra-oral Blood borne halitosis
- Extra-oral non-blood borne halitosis
- Upper respiratory tract (ENT) causes
- Lower respiratory tract causes
- Gastrointestinal halitosis
- delusional halitosis
- olfactory halucinations/neurosensory disturbance
The most common location for mouth related halitosis is the tongue. Tongue bacteria produce malodorous compounds and fatty acids, and account for 80 to 90% of all cases of mouth-related bad breath. Large quantities of naturally-occurring bacteria are often found on the posterior dorsum of the tongue, where they are relatively undisturbed by normal activity. This part of the tongue is relatively dry and poorly cleansed, and the convoluted microbial structure of the tongue dorsum provides an ideal habitat for anaerobic bacteria, which flourish under a continually-forming tongue coating of food debris, dead epithelial cells, postnasal drip and overlying bacteria, living and dead. When left on the tongue, the anaerobic respiration of such bacteria can yield either the putrescent smell of indole, skatole, polyamines, or the "rotten egg" smell of volatile sulfur compounds (VSCs) such as hydrogen sulfide, methyl mercaptan, Allyl methyl sulfide, and dimethyl sulfide.
Cleaning the tongue
The most widely-known reason to clean the tongue is for the control of bad breath. Methods used against bad breath, such as mints, mouth sprays, mouthwash or gum, may only temporarily mask the odors created by the bacteria on the tongue, but cannot cure bad breath because they do not remove the source of the bad breath. In order to prevent the production of the sulfur-containing compounds mentioned above, the bacteria on the tongue must be removed, as must the decaying food debris present on the rear areas of the tongue. Most people who clean their tongue use a tongue cleaner (tongue scraper), or a toothbrush.
There are over 600 types of bacteria found in the average mouth. Many of these can produce high levels of foul odors when incubated in the laboratory. The odors are produced mainly due to the breakdown of proteins into individual amino acids, followed by the further breakdown of certain amino acids to produce detectable foul gases. For example, the breakdown of cysteine and methionine produce hydrogen sulfide and methyl mercaptan, respectively. Volatile sulfur compounds have been shown to be statistically associated with oral malodor levels, and usually decrease following successful treatment.
Other parts of the mouth may also contribute to the overall odor, but are not as common as the back of the tongue. These locations are, in order of descending prevalence: inter-dental and sub-gingival niches, faulty dental work, food-impaction areas in between the teeth, abscesses, and unclean dentures. Oral based lesions caused by viral infections like Herpes Simplex and HPV may also contribute to bad breath.
There is some controversy over the role of periodontal diseases in causing bad breath. However, advanced periodontal disease is a common cause of severe halitosis. Waste products from the anaerobic bacteria growing below the gumline (subgingival) have a foul smell and have been clinically demonstrated to produce a very intense bad breath. Removal of the subgingival calculus (i.e. tartar or hard plaque) and friable tissue has been shown to improve mouth odor considerably. This is accomplished by subgingival scaling and root planing and irrigation with an antibiotic mouth rinse.
The second major source of bad breath is the nose. In this occurrence, the air exiting the nostrils has a pungent odor that differs from the oral odor. Nasal odor may be due to sinus infections or foreign bodies.
In general, putrefaction from the tonsils is considered a minor cause of bad breath, contributing to some 3–5% of cases. Approximately 7% of the population suffer from small bits of calcified matter in tonsillar crypts called tonsilloliths that smell extremely foul when released and can cause bad breath.
The lower esophageal sphincter, which is the valve between the stomach and the esophagus, may not close properly due to a Hiatal Hernia or GERD, allowing acid to enter the esophagus and gases escape to the mouth. A Zenker's diverticulum may also result in halitosis due to aging food retained in the esophagus.
The stomach is considered by most researchers as a very uncommon source of bad breath (except in belching). The esophagus is a closed and collapsed tube, and continuous flow (as opposed to a simple burp) of gas or putrid substances from the stomach indicates a health problem—such as reflux serious enough to be bringing up stomach contents or a fistula between the stomach and the esophagus—which will demonstrate more serious manifestations than just foul odor.
In the case of allyl methyl sulfide (the byproduct of garlic's digestion), odor does not come from the stomach, since it does not get metabolized there.
There are a few systemic (non-oral) medical conditions that may cause foul breath odor, but these are extremely infrequent in the general population. Such conditions are:
- Fetor hepaticus: an example of a rare type of bad breath caused by chronic liver failure.
- Lower respiratory tract infections (bronchial and lung infections).
- Renal infections and renal failure.
- Trimethylaminuria ("fish odor syndrome").
- Diabetes mellitus.
- Metabolic conditions, e.g. resulting in elevated blood dimethyl sulfide (Dimethylsulfidemia). 
Individuals afflicted by the above conditions often show additional, more diagnostically conclusive symptoms than bad breath.
Halitophobia (delusion halitosis)
One quarter of the patients seeking professional advice on bad breath suffer from a highly exaggerated concern of having bad breath, known as halitophobia, delusional halitosis, or as a manifestation of Olfactory Reference Syndrome. These patients are sure that they have bad breath, although many have not asked anyone for an objective opinion. Halitophobia may severely affect the lives of some 0.5–1.0% of the adult population.
Scientists have long thought that smelling one's own breath odor is often difficult due to acclimatization, although many people with bad breath are able to detect it in others. Research has suggested that self-evaluation of halitosis is not easy because of preconceived notions of how bad we think it should be. Some people assume that they have bad breath because of bad taste (metallic, sour, fecal, etc.), however bad taste is considered a poor indicator.
For these reasons, the simplest and most effective way to know whether one has bad breath is to ask a trusted adult family member or very close friend ("confidant"). If the confidant confirms that there is a breath problem, he or she can help determine whether it is coming from the mouth or the nose, and whether a particular treatment is effective or not.
One popular home method to determine the presence of bad breath is to lick the back of the wrist, let the saliva dry for a minute or two, and smell the result. This test results in overestimation, as concluded from research, and should be avoided. A better way would be to lightly scrape the posterior back of the tongue with a plastic disposable spoon and to smell the drying residue. Home tests that use a chemical reaction to test for the presence of polyamines and sulfur compounds on tongue swabs are now available, but there are few studies showing how well they actually detect the odor. Furthermore, since breath odor changes in intensity throughout the day depending on many factors, multiple testing sessions may be necessary.
If bad breath is persistent, and all other medical and dental factors have been ruled out, specialized testing and treatment is required. Hundreds of dental offices and commercial breath clinics now claim to diagnose and treat bad breath. They often use some of several laboratory methods for diagnosis of bad breath:
- Halimeter: a portable sulfide monitor used to test for levels of sulfur emissions (to be specific, hydrogen sulfide) in the mouth air. When used properly, this device can be very effective at determining levels of certain VSC-producing bacteria. However, it has drawbacks in clinical applications. For example, other common sulfides (such as mercaptan) are not recorded as easily and can be misrepresented in test results. Certain foods such as garlic and onions produce sulfur in the breath for as long as 48 hours and can result in false readings. The Halimeter is also very sensitive to alcohol, so one should avoid drinking alcohol or using alcohol-containing mouthwashes for at least 12 hours prior to being tested. This analog machine loses sensitivity over time and requires periodic recalibration to remain accurate.
- Gas chromatography: portable machines, such as the OralChroma, are currently being introduced. This technology is specifically designed to digitally measure molecular levels of the three major VSCs in a sample of mouth air (hydrogen sulfide, methyl mercaptan, and dimethyl sulfide). It is accurate in measuring the sulfur components of the breath and produces visual results in graph form via computer interface.
- BANA test: this test is directed to find the salivary levels of an enzyme indicating the presence of certain halitosis-related bacteria.
- β-galactosidase test: salivary levels of this enzyme were found to be correlated with oral malodor.
Although such instrumentation and examinations are widely used in breath clinics, the most important measurement of bad breath (the gold standard) is the actual sniffing and scoring of the level and type of the odor carried out by trained experts ("organoleptic measurements"). The level of odor is usually assessed on a six-point intensity scale.
Chronic halitosis is not well understood by most physicians and dentists, so effective treatment is not always easy to find. The following strategies may be suggested:
- Gently cleaning the tongue surface twice daily is the most effective way to keep bad breath in control; that can be achieved using a tooth brush, tongue cleaner or tongue brush/scraper to wipe off the bacterial biofilm, debris, and mucus. An inverted teaspoon may also do the job. Scraping or otherwise damaging the tongue should be avoided, and scraping of the V-shaped row of taste buds found at the extreme back of the tongue should also be avoided. Brushing a small amount of antibacterial mouth rinse or tongue gel onto the tongue surface will further inhibit bacterial action.
- Eating a healthy breakfast with rough foods helps clean the very back of the tongue.
- Chewing gum: Since dry-mouth can increase bacterial buildup and cause or worsen bad breath, chewing sugarless gum can help with the production of saliva, and thereby help to reduce bad breath. Chewing may help particularly when the mouth is dry, or when one cannot perform oral hygiene procedures after meals (especially those meals rich in protein). This aids in provision of saliva, which washes away oral bacteria, has antibacterial properties and promotes mechanical activity which helps cleanse the mouth. Some chewing gums contain special anti-odor ingredients. Chewing on fennel seeds, cinnamon sticks, mastic gum, or fresh parsley are common folk remedies.
- Gargling right before bedtime with an effective mouthwash (see below). Several types of commercial mouthwashes have been shown to reduce malodor for hours in peer-reviewed scientific studies. Mouthwashes may contain active ingredients that are inactivated by the soap present in most toothpastes. Thus it is recommended to refrain from using mouthwash directly after toothbrushing with paste (also see mouthwashes, below).
- Maintaining proper oral hygiene, including daily tongue cleaning, brushing, flossing, and periodic visits to dentists and hygienists. Flossing is particularly important in removing rotting food debris and bacterial plaque from between the teeth, especially at the gumline. Dentures should be properly cleaned and soaked overnight in antibacterial solution (unless otherwise advised by your dentist).
- Probiotic treatments, specifically Streptococcus salivarius K12 has been claimed to suppress malodorous bacteria growth, however well designed randomised control clinical trails are needed to assess this.  Certainly there is more evidence for mechanical tongue cleansing and to a lesser extent specific antimicrobial mouthwashes.
There has not been a single documented medical case of successfully cured chronic halitosis using any of the currently available mouthwashes. However, a 2008 systematic review determined the efficacy of antibacterial mouthrinses for treating bad breath. Mouthwashes often contain antibacterial agents including cetylpyridinium chloride, chlorhexidine (which can cause temporary staining of the teeth), zinc gluconate, essential oils, and chlorine dioxide. Zinc and chlorhexidine provide strong synergistic effect. They may also contain alcohol, which is a drying agent.
Other solutions rely on odor eliminators, such as oxidizers, to eliminate existing bad breath on a short-term basis.
A new approach for home treatment of bad breath is the use of oil-containing mouthwashes and two-phase (oil:water) mouthwashes. Essential oils have been found effective in reducing halitosis, and are being used in several commercial mouthwashes.
According to traditional Ayurvedic medicine, chewing areca nut and betel leaf is a remedy for bad breath. In South Asia, it was a custom to chew areca or betel nut and betel leaf among lovers because of the breath-freshening and stimulant drug properties of the mixture. Both the nut and the leaf are mild stimulants and can be addictive with repeated use. The betel nut will also cause tooth decay and dye one's teeth bright red when chewed. Both areca nut and betel leaf chewing, however, are recognised risk factors for squamous cell carcinoma (oral cancer).
In 1996, the International Society for Breath Odor Research (ISBOR) was formed to promote multidisciplinary research on all aspects of breath odors. The eighth international conference on breath odor took place in 2009 in Dortmund, Germany.
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