Bad Breath: The Most Common Causes and What Really Works
It is one of those problems that rarely brings someone to an appointment as the main reason for attending. People book for something else and, halfway through the conversation, end up asking about it. Bad breath, or halitosis, is more common than people tend to admit and, in the vast majority of cases, it originates in the mouth rather than the stomach.
That distinction is not a minor detail. It determines what actually works and what simply amounts to money wasted on mouthwashes and mints.
What Causes Bad Breath
In most cases, bad breath is caused by volatile sulphur compounds produced by bacteria that break down food debris and dead cells in the mouth. The areas where these bacteria accumulate most are the back of the tongue, the spaces between the teeth and periodontal pockets. It is estimated that around eighty to ninety per cent of cases of halitosis are of oral origin.
This means that the solution almost always involves removing the cause inside the mouth rather than simply masking the odour.
Causes Originating in the Mouth
Bacterial Build-Up on the Tongue
The back of the tongue has an irregular surface that retains bacteria, food debris and shed cells. This creates a whitish or yellowish coating, known as tongue coating, which is the most common single source of bad breath. Many people brush their teeth carefully but never clean their tongue. It is the missing step in more oral hygiene routines' of most people than we would expect.
Gum Disease
Gingivitis and periodontitis create ideal conditions for bacterial growth: pockets between the gums and teeth that a toothbrush cannot reach and where oxygen levels are low, which is exactly the environment these bacteria need.
When bad breath persists despite apparently good oral hygiene, gum disease is one of the first causes that should be investigated. We have covered the signs of gingivitis and periodontitis in detail in other articles on the blog.
Tooth Decay, Restorations and Dentures
A cavity caused by tooth decay can trap food and harbour bacteria in an area that cannot be cleaned effectively through brushing alone. The same applies to poorly fitting restorations, crowns with irregular margins or removable dentures that are not cleaned every day and outside the mouth.
Dry Mouth
Saliva is the mouth’s natural cleaning mechanism: it dilutes, washes away and neutralises. When saliva production decreases, bacteria multiply without this natural control.
This is why breath tends to be worse upon waking. During sleep, saliva production drops significantly and its cleansing effect is reduced for several hours. This morning bad breath is physiological and usually improves after brushing.
Persistent dry mouth throughout the day is different. It may be caused by medication — antihypertensives, antidepressants and antihistamines are among the groups most commonly associated with it — as well as mouth breathing, dehydration or salivary gland disorders.
In these situations, bad breath tends to be constant and does not improve with brushing alone.
Braces and Aligners
People who wear fixed braces have more surfaces where plaque can accumulate and, consequently, a higher risk of halitosis if oral hygiene is not adapted accordingly.
With clear aligners, the issue is often different: wearing the aligners without brushing the teeth after eating creates a closed environment over the tooth surfaces for several hours at a time. Regular cleaning of the aligners themselves is equally important.
Causes Outside the Mouth
Diet
Garlic, onions and certain seasonings contain sulphur compounds that are absorbed during digestion, transported through the bloodstream and eliminated through the lungs.
They are not simply present in the mouth; they are in the breath itself. This is why brushing your teeth after a meal containing garlic does not eliminate the smell.
The odour disappears once the body has finished processing and eliminating these compounds, which can take up to a day.
Very low-carbohydrate diets can cause a different effect through the production of ketone bodies, which are responsible for a characteristic sweet-smelling breath.
Smoking and Alcohol
In addition to their own odours, both smoking and alcohol reduce saliva flow and can worsen gum disease, combining two different mechanisms in the same habit.
Respiratory and Digestive Causes
Chronic sinusitis, recurrent tonsillitis and tonsil stones — small whitish deposits that form in the crypts of the tonsils — are relatively common ENT-related causes and are often overlooked.
As for the stomach, it is worth addressing one of the most persistent misconceptions about bad breath: under normal conditions, the oesophagus remains closed and odours do not pass freely from the stomach into the mouth.
Gastro-oesophageal reflux can contribute to halitosis, but it is a much less common cause than popular belief suggests. Attributing bad breath to the stomach without first investigating the mouth is one of the most frequent mistakes and can delay the correct diagnosis for months.
How Can I Tell If I Have Bad Breath?
It is difficult to assess your own breath because the sense of smell adapts to odours to which it is continuously exposed. Commonly suggested home tests, such as breathing into cupped hands, are not reliable.
A more informative method is to run a gauze pad or spoon across the back of the tongue, allow it to dry for a few seconds and then smell it. Even so, an accurate assessment is best carried out during an appointment, where the origin can be identified and an oral cause distinguished from one that may require referral to another medical specialty.
It is also worth mentioning a particular clinical situation: some people are convinced that they have bad breath when they do not, a condition known as halitophobia. In these cases, an objective assessment during an appointment can help clarify the situation.
What Really Works
Clean Your Tongue Every Day
This is the single measure with the greatest impact in many cases. Use a tongue scraper or your toothbrush, moving gently from the back of the tongue towards the front once a day. There is no need to apply excessive pressure or reach so far back that it triggers nausea. The coating that needs to be removed is superficial.
Clean Between the Teeth
A toothbrush cleans three of the five surfaces of each tooth. The remaining two, which are in contact with neighbouring teeth, can only be reached using dental floss or an interdental brush. These are precisely the spaces where plaque can remain undisturbed, which is why daily interdental cleaning can have such a noticeable effect on breath.
Treat the Dental or Gum Cause
Scaling when there is tartar and inflammation, a restoration when there is tooth decay, or adjustment or replacement when a restoration does not fit properly. As long as the source remains, no oral hygiene routine can compensate for it completely.
Keep the Mouth Hydrated
Drink water throughout the day and chew sugar-free gum to stimulate saliva production.
When dry mouth is caused by medication, it may be appropriate to speak to the treating doctor about possible alternatives or the use of saliva substitutes.
What Does Not Work
Alcohol-based mouthwashes can provide an immediate feeling of freshness, but an hour later the problem is often back. Worse still, alcohol can contribute to dryness of the oral tissues, which may aggravate the problem over time. If you use mouthwash, choose an alcohol-free formulation and regard it as a complement rather than a substitute for brushing and interdental cleaning. Mints and menthol sweets only mask the smell for a few minutes. Sugary mint sweets also add an increased risk of tooth decay. Home remedies such as rinsing with bicarbonate of soda, vinegar or lemon have no evidence of sustained effectiveness and, in the case of acidic substances, can contribute to enamel erosion. It is a poor trade-off: the original problem remains while something that cannot regenerate is gradually worn away.
When Bad Breath Justifies an Appointment
If bad breath is persistent, remains throughout the day even after brushing, or appears alongside bleeding gums, a dry mouth sensation or a constant unpleasant taste, it is worth booking an assessment.
In most cases, the cause can be identified and treated. What tends to prolong the problem is not how difficult it is to resolve, but how much time is spent trying to mask it.
