Bad Breath Despite Brushing: Why Your Tongue Is Often the Culprit
Bad breath is often seen as a sign of poor dental hygiene. Yet it can develop even in people who brush thoroughly. Dentist Dr. Tore Thomsen explains how the tongue and oral microbiome contribute to bad breath — and what new studies on probiotics reveal.
Few people like to talk about it, yet many know the problem all too well: bad breath. Those who notice it tend to reach straight for a toothbrush, mouthwash, or stick of chewing gum. But bad breath can occur even with good dental hygiene — and its causes are more varied than one might initially think.
In an interview, dentist Dr. Tore Thomsen explains why the tongue plays a particularly important role, what our oral microbiome has to do with bad breath, and which new approaches are currently under investigation. He also shares which everyday measures are worthwhile and when bad breath warrants a medical evaluation.
Where Bad Breath Actually Comes From
Bad breath is often associated with poor dental hygiene. Is that really the case?
Not exactly — "poor dental hygiene" is too simple an explanation. In the vast majority of cases, bad breath does originate in the oral cavity, but even people with good oral hygiene can be affected. The cause is especially often found on the back of the tongue, though periodontal pockets, gingivitis or periodontitis, cavities, poorly cleaned dentures, and reduced saliva flow can all play a role as well.
Typical bad breath is caused mainly by bacteria that break down proteins and sulfur-containing amino acids. This produces volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan, which smell unpleasant even at very low concentrations. The tongue serves as a particularly important reservoir for these bacteria.
What does the composition of our oral flora have to do with bad breath?
Quite a lot. What matters is not simply whether someone has "many" or "few" bacteria in their mouth, but which microorganisms predominate and what metabolic byproducts they produce.
The back of the tongue is a low-oxygen environment, which allows bacterial communities to establish themselves that break down sulfur-containing substrates and produce volatile sulfur compounds in the process.Studies show that the active microbial composition of tongue coating differs between people with and without bad breath.
We are increasingly coming to understand that bad breath can therefore also be a problem of microbial balance. That said, the oral microbiome is highly complex. There is currently no simple list of "good" and "bad" bacteria from which bad breath could be reliably predicted.
New studies suggest that certain probiotics could reduce bad breath. How well established is this now?
The data are now considerably more compelling than they were a few years ago. That said, I would not yet describe probiotics as a standard treatment.
Several systematic reviews and meta-analyses show that certain probiotics — including Streptococcus salivarius, Weissella cibaria, and various Lactobacillus strains — can improve both the concentration of volatile sulfur compounds and clinical odor ratings in the short term.
At the same time, the studies vary considerably in terms of bacterial strain, dosage, formulation, and treatment duration, and long-term data remain limited.
My conclusion would therefore be: Probiotics are a promising complementary approach, but not a substitute for treating the underlying cause.
Can the oral flora actually be shifted in a more favorable direction on a permanent basis?
The oral microbiome can be influenced — but "permanently reprogrammed" would be overstating what current evidence supports.
Oral hygiene, diet, saliva flow, smoking, medications, and inflammation all alter the conditions in which microorganisms live. Probiotics can also influence the microbial balance. However, whether this leads to a long-term, stable change in the overall oral microbiome has not yet been sufficiently demonstrated.
The goal should therefore not be to change the microbiome as drastically as possible, but rather to create a healthy oral environment in which bacteria associated with disease and odor are less able to gain a foothold.
Is the tongue underestimated in everyday oral hygiene?
In my view, clearly yes. The tongue — particularly its rear portion — is the most important reservoir of odor-producing bacteria in many patients. Its surface is highly structured and can harbor a dense coating of bacteria, food debris, and cellular material.
A recent randomized study involving 80 participants examined tongue cleaning, Streptococcus salivarius K12 probiotics, and their combination. All active groups showed a reduction in volatile sulfur compounds, with the combination producing the strongest and most sustained effect.
Earlier systematic reviews also support the finding that combining toothbrushing with tongue cleaning reduces bad breath parameters more effectively than toothbrushing alone.
For a patient with bad breath, I would therefore always assess the tongue as well and — if significant tongue coating is present — provide guidance on proper cleaning technique. The aim is emphatically not to scrub the tongue as aggressively as possible.
What Do Mouthwash, Coffee, and the Like Actually Do?
What is your view of mouthwashes for bad breath? Do they address the cause or mainly mask the problem?
That depends greatly on the product. A purely flavoring mouthwash does little more than temporarily mask the odor. Other active ingredients, however, can genuinely intervene in the mechanism behind bad breath.
Mouthwashes containing zinc, for example, can bind or neutralize volatile sulfur compounds. Active ingredients such as cetylpyridinium chloride additionally influence bacterial composition. Chlorhexidine can also be effective, but should not be used as a long-term everyday solution due to potential side effects and staining.
I therefore see mouthwashes as a supplementary measure at best. If the underlying cause is, for example, periodontitis or pronounced tongue coating, a mouthwash alone will not solve the problem.
What makes bad breath worse in everyday life — a dry mouth, longer gaps between meals, coffee, or alcohol?
Saliva is enormously important for oral health. It rinses the oral cavity, dilutes metabolic byproducts, and helps maintain oral balance. When saliva flow is reduced, odor-active substances can accumulate more easily, so dry mouth can significantly contribute to bad breath.
Diet, and in particular longer gaps between meals, can also affect breath odor. On an empty stomach, the body partly shifts its metabolism and draws more heavily on its own energy reserves, producing metabolic byproducts that can be released through exhaled air. An altered breath odor during fasting is therefore initially a physiological phenomenon and not automatically a sign of a medical condition. A recent study showed, for example, a significant increase in dimethyl sulfide in exhaled air during a multi-day fast.
Certain foods can also temporarily alter breath odor. Coffee, however, is a good example of why sweeping statements are difficult: it is frequently blamed for bad breath, yet experimental data sometimes show an inhibitory effect of certain coffee compounds on the formation of sulfur compounds.
With alcohol, the picture is more nuanced. Alcohol can, among other things, reduce saliva flow and thereby promote bad breath. The long-term effects of heavy alcohol consumption on oral health can also be a contributing factor.
When Bad Breath Should Be Medically Evaluated
When can bad breath point to gum disease or another health-related cause?
Persistent bad breath should prompt a thorough examination of the oral cavity. Bleeding gums, deep periodontal pockets, loose teeth, heavy plaque, cavities, or areas of inflammation can all be important indicators. The link between periodontitis and bad breath in particular is well established.
But not all bad breath originates in the mouth. In the ENT area, chronic inflammation of the nasopharynx, post-nasal drip, or large, heavily furrowed or cryptic tonsils can all play a role.
In deep tonsillar crypts, bacterial deposits and so-called tonsil stones can form, which can produce an unpleasant odor. The tonsils should therefore be considered when relevant symptoms are present.
If no adequate explanation can be found in either the mouth or the ENT area, other causes are considerably rarer — for example, certain metabolic disorders or diseases of the liver and kidneys.
What would you recommend to someone who suffers from persistent bad breath despite thorough brushing?
The first step is to actually establish whether bad breath is genuinely present. Some people have what is known as pseudohalitosis or halitophobia — a firm conviction that they have bad breath even though no objectively detectable bad breath is present. This can be very distressing for those affected and should by no means be dismissed as "all in their head."
Just how important this distinction is was illustrated by a German study from a multidisciplinary bad breath clinic: of 407 patients who complained of bad breath, only 72.1% actually had objectively verifiable bad breath. Among those with demonstrable bad breath, the cause was found in the oral cavity in 92.7% of cases.
A straightforward first step is an honest conversation with someone you trust. If you are unsure whether your own breath is actually unpleasant, you can ask your partner or another close person directly. This is of course no substitute for a professional examination, but it can help you better gauge your own perception.
For those with genuinely existing bad breath, the rule is: don't simply brush harder and more aggressively — instead, have the underlying cause identified first.
In a bad breath clinic, my first step would be to establish whether objectively verifiable bad breath is actually present and where it is most likely coming from. This involves examining the teeth, gums, and periodontal pockets, assessing tongue coating, and — depending on the situation — measuring volatile sulfur compounds. If the findings warrant it, an ENT cause, such as the tonsils, should also be investigated.
Treatment should then be tailored to the individual: in cases of periodontitis, treating the inflammation takes priority; with heavy tongue coating, the focus is on proper tongue cleaning; with dry mouth, the aim is to improve saliva flow or address the underlying cause. Only after that would I discuss additional measures such as specific mouthwashes or, where appropriate, probiotics.
My most important piece of advice is this: persistent bad breath is not a cosmetic problem to be masked with a peppermint flavor. It is a symptom — and a symptom should be diagnosed before it is treated.
