Bad breath (halitosis): approach
- Approach to a complaint
Nine times out of ten bad breath starts in the mouth: the coated back of the tongue, gum disease or decay. Only a few cases come from the nose, throat or body.
What it is
Halitosis is an unpleasant smell of the breath. Most is produced in the mouth by anaerobic bacteria that break down proteins into volatile sulphur compounds, mainly on the back of the tongue and in periodontal pockets. Morning breath is normal. Less often the source is the nose and sinuses, tonsil stones or tonsillitis, or rarely the body (diabetic ketoacidosis, liver or kidney failure, some metabolic disorders). Some people are convinced they have bad breath when others cannot detect it (pseudohalitosis or halitophobia).
Red flags
- Fruity smell: ketoacidosis; fishy or ammonia smell: kidney failure; musty, sweet smell (fetor hepaticus): liver failure.
- Foul breath with painful bleeding gums: necrotising gingivitis.
- Unilateral foul nasal discharge in a child: nasal foreign body.
- Halitosis with weight loss, dysphagia or bleeding needs investigation for cancer of the mouth, throat or oesophagus.
Step-by-step approach
- Ask when it started, who noticed it, morning or all day, and about dry mouth, nasal symptoms, reflux, diabetes and drugs.
- Smell the breath from the mouth and then the nose with the mouth closed: oral or nasal origin.
- Look at the tongue coating, the gums, decayed teeth, dentures, tonsils and the pharynx.
- Look for systemic clues: fruity or uraemic smell, jaundice, signs of illness.
- Treat the oral cause and review; if no source is found and others cannot smell it, consider pseudohalitosis.
Keys to the differential
- Oral origin: worse in the morning, coated tongue, gum disease or decay, improves with cleaning.
- Nasal origin: smell from the nose with the mouth closed; sinusitis or foreign body.
- Systemic origin is rare but serious: always look for the patient's general state.
Next step / Initial management
- Advise brushing teeth and the back of the tongue, cleaning between teeth, treating dry mouth and quitting tobacco.
- Refer to the dentist for gum disease, decay or ill-fitting dentures.
- Nasal or tonsillar source: treat and refer to ENT if persistent; red flags (weight loss, dysphagia, bleeding) need urgent referral.
- Suspected systemic cause: check glucose and ketones, renal and liver function.
Test yourself
Think of the answer, then tap the question to see it.
Where is most halitosis produced?
In the mouth, mainly on the coated back of the tongue and in periodontal pockets.
How can an oral and a nasal origin be told apart?
By smelling the breath through the mouth and then through the nose with the mouth closed.
What does a fruity smell on the breath suggest?
Ketoacidosis, as in diabetic ketoacidosis.
Connections
Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.
Sources: Halitosis (StatPearls Publishing (NCBI Bookshelf), 2023); Periodontal (Gum) Disease (National Institute of Dental and Craniofacial Research (NIDCR, NIH), 2024).
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Representative model, for educational purposes only.