27 Bad breath
Halitosis is the condition people are most likely to worry about privately and least likely to ask about directly. It is also, unlike everything else in this book, almost entirely absent from Delivering Better Oral Health: search the summary tables and you will find nothing.
That absence is defensible, since DBOH is a prevention toolkit for caries, periodontal disease, oral cancer and tooth wear, and halitosis is none of those. But it leaves a gap, and gaps of this kind are where the commercial market lives.
Where the smell comes from
The mechanism here is better established than most things in this book, and it is worth understanding because it makes the useless remedies obvious.
Around 80 to 90% of halitosis originates in the mouth, on the estimate of a systematic review of its causes (1), with coated tongue, periodontal disease and poor oral hygiene the main contributors. Anaerobic bacteria, living mostly on the back of the tongue and in periodontal pockets, break down proteins and release volatile sulphur compounds: hydrogen sulphide, methyl mercaptan, dimethyl sulphide. Those are the smell. They are the same compounds that make rotten eggs unpleasant, and the nose detects them at very low concentrations.
The remaining 10 to 20% is attributed to causes outside the mouth, associated with ear, nose and throat, gastrointestinal and other systemic conditions (1). An earlier draft of this chapter gave the split as 85 to 90% against 10 to 15%, with no citation and with the extra-oral share described as mostly ENT. The published figures are wider than that and the review does not say the remainder is mostly ENT.
Two consequences follow immediately.
The tongue is the main site. The dorsum of the tongue, particularly the back third, has a large surface area with papillae that hold bacteria and debris. This is why a person with excellent teeth and healthy gums can still have bad breath.
Masking is not treating, which is not the same as useless. A mint or a mouthwash that covers the smell for twenty minutes has not touched the bacteria producing it, and will not stop it coming back. An earlier draft called such products useless, which overstates it: temporary relief before a meeting or a conversation is a real thing to want, and a product can deliver it honestly. What it cannot do is address the cause, and the distinction to hold on to is between a product that helps you get through the afternoon and one that changes why your breath smells.
Morning breath is not halitosis
Morning breath is close to universal, and it is not a condition.
Salivary flow falls during sleep. Saliva clears bacteria, buffers acid and carries oxygen; anaerobic bacteria flourish without it. Overnight you get a predictable accumulation of exactly the compounds described above, which is why your mouth tastes as it does at 7am. For most people brushing and eating deal with it; breath that persists through the morning after cleaning is the kind worth raising with a dentist, because that is the pattern that suggests a cause rather than a night’s accumulation.
This is the same physiological fact that Chapter 6, Chapter 15 and Chapter 14 all lean on, which is worth noticing. Reduced overnight salivary flow is doing an enormous amount of work across dentistry for something that has been directly tested against patient-relevant outcomes remarkably rarely.
What actually helps
Ordered by how well established the reasoning is, which is not the same as how well tested it is. I want to be clear that this section rests on mechanism and clinical consensus rather than on the sort of evidence Part II demanded, and I have not conducted a systematic review of the halitosis literature.
Treat gum disease if you have it. Periodontal pockets are anaerobic environments producing exactly these compounds. If your gums bleed, this is the first thing to address, and it has the added benefit of being worth doing anyway.
Clean your tongue. Given that most of the bacteria are there, this follows directly. A tongue scraper or the back of a toothbrush, gently, once a day. The evidence base is thin and mostly measures volatile sulphur compounds rather than whether anyone noticed, but the mechanism is about as direct as mechanisms get.
Clean between your teeth. Chapter 17 found no trial measuring halitosis, and interdental spaces are stagnant sites where the same bacteria accumulate.
Address dry mouth. Medications that reduce salivary flow, of which there are many, will produce bad breath by the mechanism described above. This is worth raising with whoever prescribes them.
See a dentist to rule out the treatable. Untreated decay, a failing filling, a food trap, or a partial denture that is not being cleaned will all do it.
What does not help, or helps less than advertised
Mouthwash, mostly. An antibacterial mouthwash containing chlorhexidine, zinc compounds or cetylpyridinium chloride does more than a cosmetic one, because it reduces the bacteria rather than covering the smell. But mouthwash reaches the front of the mouth far better than the back of the tongue, which is where the problem is. And Chapter 7 gives a separate reason not to rinse with anything immediately after brushing.
Mints and chewing gum. Sugar-free gum stimulates saliva, which genuinely helps a little and briefly. Mints do nothing except smell.
Anything promising to cure halitosis systemically. Since the cause is intra-oral in most cases, a product acting elsewhere is usually treating the wrong site. That is a statement about where the problem usually is, not a diagnosis of where yours is.
Two situations where the answer is not in this chapter.
Persistent bad breath that dental treatment does not fix. After gum disease has been treated, decay restored and the tongue cleaned, a persistent problem needs ENT assessment for tonsil stones or chronic sinus infection, and occasionally investigation of systemic causes. Do not accept an indefinite program of dental appointments for something dentistry has not fixed.
Believing you have bad breath when you do not. Halitophobia is a recognized and genuinely distressing condition, in which someone is convinced they smell despite objective assessment and the reassurance of others. It is not helped by more mouthwash, and it is not a dental problem. If this describes you, it is worth saying so to a doctor, and it is far more common than most people realise.
This chapter is different from the rest of the book, and I want to be explicit about it.
Delivering Better Oral Health makes no recommendation about halitosis, so there is no recommendation to audit, no strength label to check and no evidence statement to trace. The seven-step method does not apply and there is no verdict box.
What I have written above is conventional clinical understanding, grounded in the volatile sulphur compound mechanism, which is well established, plus one systematic review of causes (1). I have not conducted a systematic search of the halitosis literature myself.
One review does bear directly on the advice in this chapter, and leaving it unmentioned would have been the error this book is about. Kumbargere Nagraj and colleagues assembled 44 randomized trials in 1,809 participants of interventions for halitosis: tongue cleaning, chewing gums, toothpastes, mouthrinses, systemic agents and combinations (2). Their finding is uncomfortable for a chapter like this one:
We found low- to very low-certainty evidence to support the effectiveness of interventions for managing halitosis compared to placebo or control … We were unable to draw any conclusions regarding the superiority of any intervention or concentration.
— Kumbargere Nagraj and colleagues, 2019 (2)
Most of those trials ran for one to four weeks; only one followed participants for three months. Three were at low risk of bias, sixteen at high, and 25 unclear.
So the practical advice above, including tongue cleaning, rests on mechanism and clinical consensus rather than on demonstrated superiority of any particular measure. It is cheap and harmless, which is why I still give it, but this is the one chapter where I am telling you what dentists generally think rather than what has been shown, and I would rather mark it than dress it up.
Full record in appraisals/searches/ch27-halitosis.md.
What this means for you
If your breath is bad in the morning, that is everybody, and brushing fixes it.
If it is bad persistently, it is almost certainly coming from your mouth, and most likely from the back of your tongue or from gum disease. Clean your tongue daily, clean between your teeth, get your gums checked, and stop buying mints.
If none of that works, ask about ENT causes rather than accepting more dentistry. And if people keep telling you your breath is fine and you cannot believe them, that is a real and treatable problem in its own right, and worth mentioning to your doctor.