Guides · General
What causes bad breath, and how does it go away?
Oral and non-oral causes of persistent bad breath, what you can do at home, the role of tongue cleaning and when an examination is needed.
About 85–90 % of bad breath originates in the mouth: the bacterial coating on the back of the tongue, gum disease, food trapped between the teeth, decay, dry mouth and poorly cleaned dentures. Tongue cleaning, interdental cleaning and scaling bring a clear improvement within a few weeks in most cases. If the odour persists despite these measures, sinusitis, tonsil stones, reflux and certain systemic diseases are investigated.
Bad breath (halitosis) affects a large share of adults, and most are unaware of it. In the great majority of cases the source is in the mouth — which means the problem can be solved with dental methods.
Oral causes
- The back of the tongue: The bacterial coating there produces sulphur compounds; the commonest cause.
- Gum disease: Periodontal pockets and bleeding are a nourishing environment for bacteria.
- Decay and old fillings: Cavities that trap food.
- Dry mouth: Less saliva means more bacteria; some medicines, mouth breathing and long fasting cause dryness.
- Dentures: Not removed at night or poorly cleaned.
- Impacted wisdom teeth: Food collecting under the gum flap covering them.
Non-oral causes
Tonsil stones, sinusitis and post-nasal drip, reflux, diabetes (an acetone smell), kidney and liver disease, certain diets (ketogenic) and smoking. If odour persists once oral causes are excluded, these areas are investigated.
Temporary and morning breath
Morning breath is normal because saliva falls during sleep; it clears with brushing and breakfast. Odour from onion, garlic and coffee lasts a few hours; because it is also released through the lungs after digestion, brushing does not remove it completely.
What you can do at home
- Brush twice a day and floss or use an interdental brush every day.
- Tongue cleaning: Gently clean the back of the tongue every morning with a scraper or brush; on its own one of the most effective steps.
- Drink plenty of water; sugar-free gum increases saliva.
- Alcohol-free mouthwash: alcohol-based ones dry the mouth and can worsen the odour.
- Remove dentures at night and soak them in a cleaning tablet.
- Stop smoking.
When to have an examination
Odour that does not improve within 2–3 weeks despite regular care, or that comes with bleeding gums, pain or altered taste, needs an examination. The dentist treats causes related to gums, decay and dentures; if the source is found not to be oral, you are referred to an ENT specialist or physician.
How do you notice your own breath?
People cannot smell their own breath because they are used to it. Simple tests: pass floss between the back teeth and smell it; scrape the back of the tongue with a clean spoon, wait a few seconds and smell; lick your wrist and smell it once dry. Honest feedback from someone close is the most reliable way. Some people believe they have bad breath when they do not (halitophobia); this calls for measurement and reassurance.
How to clean the tongue
The back third of the tongue is the main source of odour. A tongue scraper is drawn gently from the very back forward 3–5 times, rinsed each time, before brushing in the morning. The back of a toothbrush can be used, but a scraper is more effective. People with a strong gag reflex start by sticking the tongue out and breathing out.
Dry mouth and odour
Saliva washes bacteria away; when it falls, odour rises. Causes: mouth breathing, snoring, caffeine, alcohol, smoking, many medicines (antidepressants, blood-pressure and allergy drugs), stress, age. Solutions: frequent sips of water, sugar-free gum or lozenges, alcohol-free mouthwash, artificial saliva if needed; if medicine-related, discuss alternatives with your doctor.
Denture and appliance wearers
Removable dentures, night guards and clear aligners harbour bacteria; they should be brushed daily, soaked in a cleaning solution and not worn at night. The palate and tongue under a denture are brushed too.
The effect of diet
Garlic and onion pass into the blood and lungs and stay on the breath for hours; this is temporary and not solved by oral hygiene. Low-carbohydrate diets and long fasting produce an "acetone" smell. Protein-heavy diets and dairy can increase sulphur compounds; water and fibrous vegetables reduce them.
Using mouthwash correctly
Mouthwashes can mask odour; the lasting solution is removing the cause. Rinses containing chlorhexidine, cetylpyridinium and zinc reduce sulphur compounds; alcohol-based rinses dry the mouth and can worsen odour in the long run. Chlorhexidine is not used for more than 2 weeks.
Bad breath in children
Commonest causes: inadequate brushing, mouth breathing (adenoids, allergy), tonsillitis, a foreign body in the nose (one-sided foul smell!). A paediatric dental assessment and, if needed, an ENT assessment are planned together. Related: How to floss · Gum treatment
This article is for general information only; diagnosis and treatment tailored to you require a dental examination.
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