Bad Breath

What causes bad breath, and how do I get rid of it?

Halitosis is most commonly caused by infrequent or ineffective brushing and flossing — which is good news, because that is the most fixable cause. What causes bad breath and how can I fix it? is the short version of this page.

The mechanism is straightforward. When plaque is not removed from the teeth regularly, the bacteria in it produce an unpleasant odour that transfers to your breath. Food debris left in the mouth for any length of time spoils and gives off a smell of its own.

But there is no single treatment for halitosis, because treatment depends entirely on the cause. If you already have good oral hygiene and still have bad breath, the cause is something else, and the sections below on the tongue and on dry mouth are the place to start.

How common is it? Nobody should tell you they know precisely. A systematic review and meta-regression published in Clinical Oral Investigations in 2018 pooled 13 population-based studies and put the prevalence in adolescents and adults at 31.8% (95% CI 24.6–39.0%) — around a third — while stating that heterogeneity between the studies was high. Other authorities publish figures ranging from about 2.4% to 50–65%, largely without citing a source, and most population studies rely on self-report rather than measured odour.

Smile Solutions is at Level 1, 220 Collins Street, Manchester Unity Building, Melbourne CBD — see Location.

Where the smell actually comes from

The odour in most bad breath is not the plaque itself. It is a small group of gases produced when anaerobic bacteria break down proteins — from food debris, from shed cells lining the mouth, from blood in inflamed gums.

These are the volatile sulphur compounds, and the three that matter are hydrogen sulphide (the rotten-egg smell), methyl mercaptan (the one most associated with gum disease) and dimethyl sulphide (which tends to point to a cause outside the mouth altogether).

Two things follow from that, and they explain a great deal:

• The bacteria responsible are anaerobic — they thrive where oxygen does not reach. That means deep periodontal pockets, the crevices on the back of the tongue, and under the edges of failing fillings. It is why breath improves when those places are cleaned rather than when the front teeth are scrubbed harder.
• They feed on protein, not sugar. This is the opposite of what causes decay, which is why someone with no cavities at all can still have significant halitosis.

The tongue is usually the single biggest source

In people with no gum disease, the coating on the back of the tongue is the largest single source of oral malodour. In a study of 2,000 consecutive patients attending a multidisciplinary bad-breath clinic in Leuven, Belgium, published in the Journal of Clinical Periodontology in 2009, an oral cause was identified in 76% of attenders — tongue coating in 43%, gingivitis or periodontitis in 11%, and both together in 18%. Those figures describe a dedicated clinic whose patients had been complaining for a mean of seven years, not the general population.

The tongue's upper surface is covered in papillae, and the resulting rough terrain holds a film of bacteria, shed cells and food residue. The posterior third — the part near the throat, which almost nobody cleans — is the least oxygenated and the most heavily coated.

Be clear about what cleaning the tongue does and does not do. healthdirect Australia states that cleaning your tongue with a scraper or tongue cleaner “does not treat halitosis, but it can help to remove bacteria from your mouth”. The Australian Dental Association's consumer site reports that a 2019 review “found no evidence that cleaning your tongue, using several different methods including mouthwash or chewing gum, were effective for managing the cause of halitosis” — although a key-message box on that same ADA page says tongue cleaning can help reduce bad breath, so the ADA is not internally consistent on the point. That review is Cochrane's Interventions for managing halitosis (44 trials, 1,809 participants): for mechanical tongue cleaning against none it found a mean difference in dentist-scored breath of −0.20 (95% CI −0.34 to −0.07; 2 trials, 46 participants), rated very low certainty, and was “unable to draw any conclusions regarding the superiority of any intervention or concentration”.

So clean the tongue for the bacteria it removes — not on the understanding that it is a treatment in its own right.

How to clean it properly — and Should I use a tongue scraper? covers the choice of tool:

• Use a tongue scraper rather than a toothbrush where you can; it removes more coating with less gagging. A soft-bristled brush is an acceptable alternative, and the ADA says to use water to lubricate the process so it does not drag on the surface.
• Start as far back as you can tolerate and draw forward. The back is the part that matters — scraping only the tip achieves very little.
• Rinse the scraper between strokes, and stop at four or five.
• Gently. The aim is to remove the coating, not to abrade the tongue. Bleeding or soreness means too much pressure.
• The top surface only. An international consensus workshop reported in the Journal of Breath Research in 2014 recommends cleaning the tongue dorsum with the focus on its posterior part, not the lateral borders, and gently — and states that where there is no coating, tongue cleaning should not be advocated at all.
• Gagging is common at first and usually settles over a week or two as you work slightly further back each day.

A tongue coating that will not shift, or a coating on one side only, is worth having looked at rather than scrubbed harder.

The other contributing factors

• Dental decay or gum infection
• Gum disease — gingivitis or periodontitis
• Strong-smelling foods — garlic, onion, cauliflower
• Acid reflux or other digestive issues
• Medical conditions — kidney failure, metabolic or biochemical disorders
• Smoking or extreme dieting

Add to that list the things patients most often have and least often suspect: failing fillings and leaking crown margins that trap debris, partial dentures that are not cleaned overnight, food packing between teeth where a contact point has opened up, and partly erupted wisdom teeth with a flap of gum over them that collects debris and cannot be brushed clean. See Tooth Fillings and Wisdom Teeth.

Gum disease and breath

Periodontal pockets are close to a perfect habitat for the bacteria that cause malodour: deep, warm, low in oxygen, and continuously supplied with protein from inflamed tissue and bleeding.

That is why bad breath together with gums that bleed when you brush is a different proposition from bad breath on its own. It suggests a cause that will keep producing odour until the pockets themselves are treated, and one that is doing damage while it does so. What Is Gum Disease? explains what is happening below the gumline.

If that describes you, read Bleeding Gums next, and have the gums measured rather than starting with mouthwash. Where the disease is advanced, care may involve a specialist periodontist.

Dry mouth: the most commonly missed cause

Dry mouth (xerostomia) is one of the leading causes of halitosis, and it is frequently overlooked by people who assume their hygiene must be at fault. My mouth always feels dry! What can I do? sets out the practical measures.

Saliva clears food and debris from the mouth after eating. If you are not producing enough of it, that cleansing action is limited and food simply stays in the mouth longer than it should. Saliva also carries oxygen and buffers acid, so a dry mouth is chemically friendlier to exactly the anaerobes described above.

Dry mouth has many causes — medications, medical conditions, dehydration, breathing through the mouth, and smoking among them. If your hygiene is genuinely good and the problem persists, this is worth raising with your dentist specifically.

Bring a list of your medications to the appointment. A large number of common prescriptions reduce saliva flow, and the connection is easy to miss if nobody looks at the list. Never stop a prescribed medication on your own account — that is a conversation for your doctor, and there are usually ways to manage the dryness instead.

Mouth breathing deserves a mention of its own. Sleeping with the mouth open dries the tissues overnight and is a common reason for breath that is bad in the morning and fine by mid-morning — see Mouth Breathing: The Silent Habit. If it comes with snoring or unrefreshing sleep, that is worth raising with your doctor, and Snoring & Sleep Apnoea sets out what dentistry can and cannot contribute.

Morning breath is normal

Saliva flow drops to almost nothing during sleep. Bacteria are left undisturbed for seven or eight hours in a drying mouth, and the result is the familiar morning odour.

That is physiology, not disease. healthdirect Australia puts it plainly: it is normal to have bad breath when you wake up, and it usually goes away once you have had something to drink or cleaned your teeth — but bad breath that does not go away “may be a sign of another medical condition”. Breath that is unpleasant through the day, despite reasonable hygiene, is the kind worth investigating.

Why some foods cause it and why brushing does not help

The aromas in foods like garlic and onion, and drinks like coffee and alcohol, are absorbed into the bloodstream and transferred to the lungs. From there the scent escapes through your mouth as you breathe.

That means the smell is not coming from your mouth at all, and no amount of brushing, rinsing or mints will remove it. It lasts as long as the compounds remain in your system — which for garlic can be the better part of a day.

The same route explains a few distinctive smells that point away from the mouth entirely: the sweet, fruity breath sometimes described in poorly controlled diabetes, the ammoniacal smell associated with advanced kidney disease, and the characteristic odour of severe liver disease. These are medical findings, not dental ones, and they belong with your doctor.

Why smoking makes it worse in two ways

Smoking dries up saliva and causes bacteria to accumulate in the mouth — attacking the problem from both directions at once.

The smoke and its chemicals are also inhaled deep into the lungs, so the scent is exhaled afterwards in the same way as food compounds. Smoking also makes gums bleed less while they are becoming more diseased, which removes the warning sign people usually rely on.

Why you cannot smell your own breath

This is a genuine physiological limitation, not a failure of attention. The olfactory system adapts to a continuous odour within a couple of minutes and stops registering it. Your own breath is the most continuous odour you will ever be exposed to.

Cupping a hand over your mouth and sniffing does not work, for the same reason. The two informal checks that come closer:

• Lick the back of your wrist, let it dry for ten seconds, and smell it. This samples saliva from the front of the mouth — the mildest part.
• Smell the floss after cleaning between the back teeth. This samples the place the smell actually comes from, and it is the more informative of the two — and if you are not flossing at all, Is flossing really that important? makes the case.

Neither is a diagnosis. The reliable way to find out is to ask someone you trust, or to be assessed.

How halitosis is assessed professionally

There is more method here than most people expect:

• Organoleptic assessment — a trained assessor scores the breath directly. Crude-sounding, but it remains the reference standard: the 2014 international consensus workshop states that organoleptic measurement is mandatory even where an instrument is also used, and that one calibrated judge is sufficient.
• Sulphide monitoring — a portable device gives a numeric reading of volatile sulphur compounds. The same consensus treats instrumental detection as not mandatory, and it is useful mostly for tracking change over time.
• Examining where it comes from — the consensus says the first-appointment test should always be performed on both oral and nasal air, because comparing the two separates an intra-oral cause from a nasal or blood-borne one. healthdirect describes the same manoeuvre. A tongue-coating score, periodontal charting and a check of every restoration margin then locate an oral cause precisely.

Some people who are certain they have bad breath do not have it. In the Leuven series, 16% of attenders had pseudo-halitosis or halitophobia — no odour detectable on assessment — four times the 4% found to have an ear, nose and throat or other extra-oral cause. It is a recognised presentation and deserves to be taken seriously rather than dismissed: the 2014 consensus routes halitophobia to a clinical psychologist or psychiatrist rather than to further dental treatment, and healthdirect likewise suggests speaking to your doctor. The right first step is still an honest assessment, because knowing the objective answer is where any useful conversation starts.

Eight steps to treat and prevent bad breath

These are expanded in 7 Ways To Avoid Bad Breath.

1. Brush twice daily with fluoridated toothpaste
2. Floss daily to remove bacteria your toothbrush cannot reach
3. Minimise strongly scented foods and drinks
4. Stay hydrated to prevent your mouth drying out
5. Schedule six-monthly professional dental cleans
6. Clean your tongue gently — for the bacteria it removes, not as a treatment in its own right
7. Chew sugar-free gum between meals — it stimulates saliva
8. Avoid smoking

Practising good oral hygiene is the crucial first step. The tongue is the part most often skipped, and it holds a substantial share of the bacteria involved.

Where the toothbrush does not reach matters as much as how long you brush. Between the back teeth is where flossing or an interdental brush earns its keep, and interdental brushes clear more plaque than floss wherever the space is wide enough to take one — a hygienist can size them for you.

A note on mouthwash: a strongly alcoholic rinse can make dry mouth worse, and masking an odour is not the same as removing its cause — see The truth and myths about mouthwashes. Cochrane's 2019 review is sobering on rinses too: only one comparison in it reached even low-certainty evidence, brushing plus a cetylpyridinium chloride mouthwash against brushing alone (mean difference −0.48, 95% CI −0.72 to −0.24; 1 trial, 70 participants). If you are using mouthwash daily to manage breath, that is a reason to be examined, not a solution.

What a professional clean does that brushing cannot

Home care removes soft plaque. It does not remove calculus — plaque that has mineralised onto the tooth and can no longer be brushed off. Calculus is porous, holds bacteria, and sits precisely where the anaerobes do best: below the gum line.

A hygienist appointment removes it above and below the gum, cleans the margins of existing restorations, measures the gums so a periodontal cause is not missed, and shows you which of your own techniques is falling short. See Dental Cleans & Hygienists and Your Smile Solutions dental hygienist visit: what to expect.

If it persists despite all of that

See your dentist or hygienist. They can diagnose the cause and advise on reversing it.

Three specific situations have specific answers:

• Chronic sinusitis — a saline nasal spray may help. Post-nasal drip delivers a steady protein supply to the back of the tongue, which is why sinus problems and breath complaints travel together.
• Tonsil stones (tonsilloliths) — small, pale, extremely malodorous concretions in the tonsillar crypts. They are harmless, easily missed, and a classic cause of breath that survives perfect dental hygiene. An ENT opinion is the usual next step if they recur.
• Overgrowth of sulphur-producing anaerobic bacteria — a course of antibiotics effective against anaerobes may be considered. This is a prescribing decision for your treating practitioner, not a self-treatment, and it is mentioned here only so you recognise the approach if it is offered to you.

If the problem appears to be systemic rather than oral, we can refer you to a specialist who can identify and address the underlying cause.

When bad breath is a reason to be seen sooner

Most halitosis is a hygiene or dryness problem. Some of it is a signal. Book an examination promptly, rather than waiting for a routine check-up, if bad breath comes with:

• bleeding, swollen or receding gums, or teeth that feel loose — possible periodontitis
• a persistent bad taste, facial swelling, or pain on biting — possible abscess
• an ulcer, red or white patch, or lump in the mouth that has not healed in two weeks — see Oral cancer: signs, risk factors and how your dentist can help
• a sudden change with no dietary explanation, particularly alongside weight loss, reflux symptoms or unusual thirst

These are reasons for an examination, not a diagnosis. Facial swelling with fever, or swelling that is closing your eye or affecting swallowing or breathing, is a medical emergency — call 000 or attend a hospital emergency department. For urgent dental problems, see Emergency Dentistry.

What to bring, and what to expect

• A list of your medications, including anything over the counter
• Any medical conditions and recent changes to them
• When you notice it — mornings only, all day, after meals, or reported by someone else
• What you have already tried, and whether any of it helped
• Do not brush, rinse, scrape or use mints in the hours before the appointment. It is a natural instinct and it removes the very thing that needs assessing. The 2014 consensus goes further for a first breath assessment: no tongue cleaning for 24 hours beforehand, and nothing in the mouth but water on the morning of it.

Questions worth asking:

• Is this coming from my gums, my tongue, or somewhere else?
• Are any of my fillings or crowns trapping debris?
• Do my gums need measuring?
• Is anything I take causing dry mouth?
• Is this dental at all, or should I see my doctor?

Common questions

Everyone keeps telling me it must be coming from my stomach. Is it?

Almost certainly not, and this is the single most persistent misconception about bad breath.

A review of extra-oral halitosis published in the British Dental Journal is blunt about it: “The gastro-intestinal tract can only indirectly (haematogenic) influence bad breath. A majority of patients and physicians still abusively believes that halitosis originates from the stomach. The latter is only correct in <0.5% of the cases.” The oesophagus is normally closed; gas does not simply travel up from the stomach on the breath.

There are real exceptions, and they are specific rather than vague:

• Severe regurgitation. The same review states that where severe regurgitation is present, halitosis will be present with it — usually alongside coughing, post-nasal drip and heartburn. That is a reason to have reflux properly assessed, not a reason to buy stronger mouthwash. healthdirect lists gastro-oesophageal reflux disease among the medical causes.
• A pharyngeal pouch (Zenker's diverticulum), which traps food and produces a chronic unpleasant odour. Its incidence is given as less than 0.1%, and it is only diagnosed in patients over 65.
• Helicobacter pylori. The evidence here is genuinely unresolved. The review notes that laboratory studies show the organism producing sulphur compounds, and that when gastrointestinal disease was treated most halitosis complaints resolved — but also that “there is no 100% clear correlation found” between H. pylori ulcers and halitosis, and that a comparative study in children was not statistically significant. Its conclusion is that more research is needed.

The practical consequence: if your breath is the problem, the mouth is where the investigation starts. Treating a presumed stomach cause while a tongue coating or a periodontal pocket goes unexamined is the most common way people spend years not getting anywhere.

I've tried every mouthwash, mint, gum and toothpaste on the shelf. Is any of it actually proven?

This is the most useful and least commercial answer on the page: the evidence for all of it is weak, and the honest summary is that nobody knows which product works best.

Cochrane's 2019 review Interventions for managing halitosis pooled 44 trials and 1,809 participants across eight categories of intervention. Its own plain-language conclusion is: “We do not have enough evidence to say which intervention works better to control bad breath.” Only 3 of the 44 trials were at low overall risk of bias, 16 were at high risk and 25 unclear.

The individual results give the flavour:

• Chewing gum (0.6% eucalyptus versus placebo gum): mean difference −0.10, 95% CI −0.31 to 0.11 — the interval crosses zero, so no demonstrated benefit. One trial, 65 participants, very low certainty.
• A chlorhexidine and zinc acetate mouthwash versus placebo: −0.20, 95% CI −0.58 to 0.18 — again crossing zero. One trial, 44 participants, very low certainty.
• A mushroom-extract tablet (1,000 mg champignon): −1.07, 95% CI −14.51 to 12.37. One trial, 40 participants, very low certainty. That confidence interval is so wide it tells you almost nothing.
• A triclosan toothpaste: −3.48, 95% CI −3.77 to −3.19 — a large apparent effect, but from a single trial of 81 participants at very low certainty, which is not a basis for a recommendation.
• Brushing plus a cetylpyridinium chloride mouthwash versus brushing alone was the only comparison in the whole review to reach even low certainty: −0.48, 95% CI −0.72 to −0.24, one trial, 70 participants.

The sources disagree here, and it is worth seeing the disagreement rather than a tidy answer. healthdirect Australia suggests choosing a mouthwash containing peppermint, zinc or chlorhexidine, and other reviews describe those ingredients as having proven efficacy — while Cochrane, looking at the trials themselves, found only very low certainty and a confidence interval crossing zero for exactly that kind of rinse. The FDI World Dental Federation additionally lists probiotics and laser therapy among “advanced treatments”, which no trial evidence in this corpus supports.

On mints specifically, healthdirect is clear that they “can help with bad breath in the short-term” but that sugared mints increase the risk of tooth decay — so a habit built on them trades one problem for another. Sugar-free gum is the better option, and the reason it helps is saliva flow rather than any deodorising effect.

None of this means products are useless. It means no product has been shown to outperform another, and none of them addresses a cause. If a rinse is what stands between you and a conversation at work, use it — and book the examination anyway.

Could it be my sinuses rather than my mouth?

It is a genuinely common cause, and one most people never connect.

The British Dental Journal review reports that in chronic sinusitis, 50–70% of patients complain of oral malodour. healthdirect lists sinus infection, tonsillitis and throat infection among the medical causes of persistent halitosis, and includes “a runny nose, or other symptoms of a sinus infection” among the symptoms that may accompany it.

The mechanism is the post-nasal drip already described above: a continuous supply of protein-rich secretions running onto the back of the tongue, which is precisely the low-oxygen surface where the odour-producing bacteria do best. The same anatomy explains the tonsil stones mentioned earlier.

This is why the first professional assessment compares oral air with nasal air. If the nasal air smells and the oral air does not, the problem is above the palate and the referral is to an ear, nose and throat specialist rather than to more dentistry. Blocked nose, facial pressure, a persistent post-nasal drip or repeated sinus infections alongside bad breath are all reasons to mention it to your doctor as well as your dentist.

I wear a denture or a plate. Is that the cause?

It can be, and the detail that matters is overnight wear.

The British Dental Journal review names “unclean acrylic dentures (worn at night or not regularly cleaned or with rough surfaces)” among the odontogenic causes of bad breath. A study of older adults cited in the same review found overnight denture wear significantly related to oral malodour, alongside tongue plaque, oral dryness and burning mouth. healthdirect's prevention advice is the same in plainer words: make sure dentures fit well, clean them regularly, and take them out before you go to sleep.

The reason is the material. Acrylic is porous and, once it has been worn and cleaned for years, microscopically rough — an excellent surface for a bacterial film, and one a toothbrush alone does not fully clear. A denture left in overnight gives that film eight undisturbed hours in a mouth that is already drying out.

Three practical points. A denture that no longer fits well traps food under it, so a poor fit is a breath problem as well as a comfort one. A partial denture puts the same porous surface against your remaining natural teeth, which is why the gums around the clasps need particular attention. And if you have had the same denture for many years, ask whether the surface itself has become the problem — see Dentures.

How long will it take to fix, and will one clean sort it out?

The honest answer is that it depends entirely on which cause you have, and that nobody can quote you a reliable timeline from the evidence.

That second part is worth being explicit about. In the Cochrane review, most trials followed participants for only one to four weeks, and just one of the 44 reported results at three months. So the research literature can say something about short-term change and almost nothing about durability. Any page that promises a fixed number of days is inventing it.

What can be said by cause:

• A hygiene or tongue-coating cause responds to a change in technique, and you would expect to notice a difference within days to a couple of weeks of actually doing it differently — not from buying a new product.
• A periodontal cause does not resolve until the pockets are treated, and periodontal treatment is staged over appointments with a review afterwards to check the pockets have actually closed. One clean will not do it, and a clean that leaves the pockets untreated can make the breath seem better for a fortnight while the disease continues.
• A dry-mouth cause improves when the dryness is addressed, which may mean a conversation with your doctor about the medication list rather than anything dental.
• A cause outside the mouth — sinuses, reflux, tonsil stones — will not improve with dental treatment at all, which is exactly why the assessment is done before the treatment is chosen.

So a single hygienist appointment may be enough, and it may also be the visit that identifies why it is not. The useful question to ask at the end of it is: what did you find, what are we treating, and when should this have changed?

It is affecting my confidence at work and around people. Is that worth mentioning to anyone?

Yes, and it is a recognised part of the problem rather than an overreaction.

healthdirect Australia addresses it directly: halitosis “can affect the way you feel about your personal appearance or make you feel worried that other people may find your breath unpleasant. This can sometimes lead to anxiety when you're around other people.” Its advice is that if halitosis is affecting your mental health or social wellbeing, you should speak to your doctor about your symptoms and your feelings — and that they may recommend seeing a psychologist.

Two things are worth separating. Where there is a measurable odour, the psychological distress is a consequence of a treatable physical problem, and both parts deserve attention rather than one being treated as the real issue. Where assessment finds no odour — the pseudo-halitosis and halitophobia group described above, 16% of attenders in the Leuven series — the distress is the condition, and continuing dental treatment will not touch it.

Which of those applies to you is not something you can determine by worrying about it, and it is the strongest practical argument for being assessed properly. Knowing the objective answer is what makes the next conversation, with whoever it is with, a useful one.

Related pages: General Dentistry, Bleeding Gums, Dental Cleans & Hygienists, Tooth Fillings, Wisdom Teeth, Toothache & Tooth Pain, Specialist Periodontists, Emergency Dentistry, Contact Us.

Practical details

General information only — it is not a diagnosis, a treatment plan or a promise of any particular clinical outcome, and it does not replace advice from your treating practitioner. Causes of halitosis vary between individuals and several can be present at once; persistent bad breath needs to be examined rather than self-treated, because some of its causes are conditions that get worse while they are being masked. Any medicine mentioned here is a matter for your treating practitioner to decide, not something to seek or start on the basis of this page.

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