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Persistent bad breath — halitosis — is common, rarely discussed, and in the great majority of cases comes from the mouth rather than from the stomach or anywhere else.
That is good news, because it means it is usually addressable.
Where the smell comes from
Bacteria break down protein and release volatile sulphur compounds. Those are the smell. They thrive where there is no oxygen and plenty of debris: deep in the tongue coating, between teeth, under the gum margin, and inside gum pockets.
The usual sources, in order
Tongue coating. The back of the tongue has a deeply textured surface that holds a biofilm. This is the biggest single contributor, and it is routinely missed because people clean their teeth and stop.
Gum disease. Inflamed, bleeding gums and deep pockets are a reliable source, and one that will not resolve without treating the gums.
Food trapping, usually from an area that is not being cleaned interdentally, a broken filling, or an overhang at the edge of a restoration.
Dry mouth. Saliva clears bacteria and debris constantly. Less saliva means more smell — which is exactly why morning breath exists, since saliva flow drops overnight. Medication-induced dry mouth, mouth-breathing, snoring and dehydration all do the same thing.
Decay, particularly large cavities holding food.
Tonsils, occasionally — tonsil stones, or an infection. Worth knowing because none of the advice below will touch it, and it is the one cause on this list that is not a dental problem at all.
What is usually not the cause
Stomach problems are blamed often and responsible rarely — the oesophagus is normally closed, so gastric odour does not continuously reach the mouth. Persistent reflux is a genuine exception.
Smoking, garlic, onions, coffee and alcohol all cause breath odour, but that is transient and not the same condition.
What to do about it
- Clean your tongue. A tongue scraper, or the back of a toothbrush, drawn gently from as far back as you can comfortably reach, forwards. Rinse and repeat a few times. Once a day. For many people this is the single biggest change.
- Clean between your teeth daily. Smell the floss — unpleasant, but it tells you exactly where the problem is.
- Brush twice daily for two minutes, including the gum margin.
- Drink water through the day, and chew sugar-free gum if your mouth is dry — it stimulates saliva.
- Have your gums assessed, if bleeding is present.
Give that a fortnight of honest effort before concluding it has not worked.
How to tell whether you have it
Self-assessment is notoriously unreliable: you acclimatise to your own smell. Licking the inside of your wrist, letting it dry for ten seconds and smelling it is a crude but reasonable test. Asking somebody you trust is better.
Some people are convinced they have bad breath when objectively they do not. That is a recognised and distressing condition in its own right, and it is worth saying out loud to a clinician rather than escalating mouthwash.
Brushing harder is not the answer. Cleaning the tongue and between the teeth usually is.