Causes courantes de la mauvaise haleine
Revu par Dr Krishna Vakharia, MRCGPDernière mise à jour par Dr Hayley Willacy, FRCGP Last updated 31 oct. 2022
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Dans cette série :Halitose
Most cases of bad breath (halitosis) come from germs (bacteria) or debris that build up within the mouth.
At a glance
Bad breath, also known as halitosis, is often caused by bacteria in the mouth.
It can also be caused by certain foods, drinks, medicines, smoking, and dry mouth.
Morning bad breath is common due to a dry mouth overnight.
Good oral hygiene, including regular brushing, flossing, and tongue cleaning, can help.
Medical conditions like infections or diabetes can sometimes be a cause, but this is less common.
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What causes bad breath?
Morning bad breath
Most people have some degree of bad breath after a night's sleep. This is normal and occurs because the mouth tends to get dry and stagnate overnight. This usually clears when the flow of saliva increases soon after starting to eat breakfast.
Dry mouth (xerostomia)
Bad breath associated with a bouche sèche is caused by a reduction in the cleansing mechanism of the mouth as a result of reduced flow of saliva from the salivary glands. There are many causes of a dry mouth contributing to bad breath. The most common cause is after a night's sleep (discussed above). Dry mouth may also occur:
Due to a lack of fluid in the body (déshydratation).
As a side-effect of some medicines (for example, antidépresseurs tricycliques).
As a symptom of some diseases (such as syndrome de Sjögren).
Following radiotherapy to the head and neck region.
Artificial saliva is available; all can be bought over the counter at pharmacies and some can be prescribed on the NHS for certain conditions.
Foods, drinks and medicines
Chemicals in foods can get into the bloodstream and then be breathed out from the lungs. Most people are familiar with the smell of garlic, spicy foods and alcoholic drinks on the breath of people who have recently eaten or drunk these. Various other foods and medicines can cause bad breath. This type of bad breath is temporary and easily cured by not eating the food.
If a medicine is the cause of bad breath, then discuss possible alternatives with your doctor. Medicines that have been associated with bad breath include:
Betel.
Chloral hydrate.
Nitrites and nitrates.
Dimethyl sulfoxide.
Some chemotherapy medicines.
Phenothiazines.
Amfetamines.
'Water' tablets (diuretics).
Check the list of side-effects on the leaflet that comes with your medicine if you think it might be causing bad breath.
Tabagisme
Most non-smokers can tell if a person is a smoker by their breath. . Stopping smoking is the only cure for this type of bad breath. Smoking tobacco products also increases the risk of developing les maladies des gencives - another cause of bad breath.
Diets
Crash dieting or fasting can cause a sickly sweet smell on the breath. This is due to chemicals called ketones being made by the breakdown of fat. Some ketones are then breathed out with each breath. Low-carbohydrate and keto diets also can cause this sort of bad breath.
Medical causes
Medical causes, other than health problems in the mouth, are relatively uncommon. Possible causes include:
Nasal problems. For example, a lump (polyp) in the nose or a small object stuck in a nostril (occurs most commonly in children) can cause a bad smell. In this situation, the smell tends to occur only, or more severely, when you breathe out through your nose. It is not so noticeable when you breathe out through your mouth.
Throat infections such as amygdalite.
Mouth infections, such as abcès dentaires.
Infections ou tumours of the lung.
Reflux of acid from the stomach ou a stomach infection called Helicobacter pylori.
Severe kidney or liver problems.
Fish odour syndrome (trimethylaminuria). This is a rare medical cause but worth being aware of. It typically causes breath and body odour that is often like a fishy smell. It occurs because the body loses the ability to properly break down trimethylamine which is found in certain foods. There is then a build-up of trimethylamine in the body which is released in sweat, urine and breath. Urine and blood tests can help to confirm this diagnosis if it is suspected.
In these medical cases, there are usually other symptoms that would indicate the cause. For example, a blocked nose, sinus pain, chest symptoms, a high temperature (fever), etc. If you are otherwise well and have no other symptoms apart from bad breath, the smell is likely to be coming from a build-up of bacteria in the mouth and other medical causes are unlikely.
Bad breath caused by germs (halitosis)
Retour au sommaireIn most people who have bad breath (halitose), the bad smell is thought to come from germs (bacteria) and debris within the mouth.
As the bacteria break down proteins and other debris in the mouth, they release foul-smelling gases. One or more of the following may contribute to the build-up of bacteria, debris and bad breath:
Food stuck between teeth and gums
Normal teeth brushing may not clear bits of food which can get stuck between teeth. The food then rots and becomes riddled with bacteria. In addition to regular cleaning with fluoride toothpaste, flossing between the teeth (or using interdental brushes) can clear and prevent this problem.
If you wear dentures, they should be removed and cleaned every night.
Plaque, tartar (calculus) and gum disease
Plaque dentaire is a soft whitish deposit that forms on the surface of teeth. It forms when bacteria combine with food and saliva. Plaque contains many types of bacteria. Calculus is hardened calcified plaque. It sticks firmly to teeth. Gum disease means infection or inflammation of the tissues that surround the teeth. If your gums look inflamed, or regularly bleed when you clean your teeth, you are likely to have gum disease. The severity can range from mild to severe.
There is some evidence that antibacterial mouthwashes (such as those containing chlorhexidine) may also be useful in preventing bad breath. Be aware that these may discolour your teeth or dentures. These can be bought over the counter.
Coating on the back of the tongue
In some people, a coating develops on the back part of the tongue. It is not clear why this occurs. It may be from mucus that drips down from the back of the nose (postnasal drip). The coating can contain many bacteria. This explains why bad breath can sometimes occur in people with otherwise good oral hygiene. It is recommended that the tongue is cleaned every night with a proper utensil (such as a tongue scraper), rather than a toothbrush.
Tonsil stones (tonsilloliths)
Calculs amygdaliens are are clusters of calcified material that form in the tonsillar crypts, or crevices of the tonsils. They are made up mostly of calcium but can contain other ingredients such as magnesium and phosphorus, and can feel like a small lump in the tonsils. Rarely harmful, they can be a nuisance and hard to remove and can often cause bad breath.
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Questions fréquemment posées
Can certain medications directly cause bad breath, and if so, what should I do?
Yes, some medicines can cause bad breath. Examples include certain chemotherapy medicines, diuretics ('water' tablets), and tricyclic antidepressants. If you suspect a medicine is the cause, you should check the side-effects listed on the leaflet that comes with your medication. You can also discuss possible alternatives with your doctor.
I've noticed a strange sickly sweet smell on my breath since starting a new diet. What could be causing this?
A sickly sweet smell on the breath can be caused by crash dieting, fasting, or following low-carbohydrate and keto diets. This smell is due to chemicals called ketones, which are produced when your body breaks down fat. Some of these ketones are then breathed out.
Can issues with my nose or sinuses lead to bad breath?
Yes, problems like a lump (polyp) in the nose, a small object stuck in a nostril (especially in children), or sinus infections can cause a bad smell. In cases of nasal issues, the smell tends to be more noticeable when breathing out through the nose rather than the mouth.
Is it true that bad breath can sometimes be a sign of a more serious medical condition?
While uncommon, bad breath can occasionally be linked to more serious medical conditions beyond dental problems. These can include infections or tumours of the lung, severe kidney or liver problems, diabetes, and reflux of acid from the stomach. However, in these cases, there are usually other symptoms that would indicate the cause, such as a blocked nose, chest symptoms, or a high temperature.
I clean my teeth regularly, but still have bad breath. Could there be another reason?
Even with good oral hygiene, bad breath can occur. A common cause is a coating that develops on the back of the tongue, which can harbour many bacteria. This can sometimes be due to mucus dripping from the back of the nose (postnasal drip). Cleaning your tongue every night with a proper utensil, like a tongue scraper, is recommended.
What are tonsil stones and how do they relate to bad breath?
Tonsil stones, also known as tonsilloliths, are small clusters of calcified material that form in the crevices of your tonsils. They are mainly made of calcium but can also contain other substances. Although usually harmless, they can be a nuisance, hard to remove, and are a common cause of bad breath.
Lectures complémentaires et références
- Halitose; NICE CKS, septembre 2024 (accès réservé au Royaume-Uni)
- Izidoro C, Botelho J, Machado V, et al; Revisiting Standard and Novel Therapeutic Approaches in Halitosis: A Review. Int J Environ Res Public Health. 2022 Sep 8;19(18). pii: ijerph191811303. doi: 10.3390/ijerph191811303.
- Jamali Z, Alipour M, Ebrahimi S, et al; Effect of Halita mouthwash on oral halitosis treatment: A randomized triple-blind clinical trial. J Dent Res Dent Clin Dent Prospects. 2019 Winter;13(1):31-35. Epub 2019 Apr 24.
- Acar B, Berker E, Tan C, et al; Effects of oral prophylaxis including tongue cleaning on halitosis and gingival inflammation in gingivitis patients-a randomized controlled clinical trial. Clin Oral Investig. 2019 Apr;23(4):1829-1836. doi: 10.1007/s00784-018-2617-5. Epub 2018 Sep 13.
- Poniewierka E, Pleskacz M, Luc-Pleskacz N, et al; Halitosis as a symptom of gastroenterological diseases. Prz Gastroenterol. 2022;17(1):17-20. doi: 10.5114/pg.2022.114593. Epub 2022 Mar 18.
- Kauss AR, Antunes M, Zanetti F, et al; Influence of tobacco smoking on the development of halitosis. Toxicol Rep. 2022 Mar 6;9:316-322. doi: 10.1016/j.toxrep.2022.02.012. eCollection 2022.
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About the authorView full bio

Dr Mary Harding, MRCGP
Médecin généraliste, Auteur médical
BA, MA, MB, BChir, MRCGP, DFFP
Dr Mary Harding qualified from Cambridge University medical school in 1989.
About the reviewerView full bio

Dr Krishna Vakharia, MRCGP
Chief Medical Officer for Health, Optum UK
MBChB, MRCGP(2013), BMedSci (hons), DFSRH, DRCOG, PGDipDerm (Distn)
Dr Krishna Vakharia is an NHS GP. She is also a regular examiner for the postgraduate Diploma in Practical Dermatology at Cardiff University as well as being the Chief Medical Officer for health at Optum UK.
Historique de l'article
Les informations sur cette page sont rédigées et examinées par des cliniciens qualifiés.
Prochaine révision prévue : 30 oct. 2027
31 oct. 2022 | Dernière version
6 Jul 2017 | Publié à l'origine
Écrit par :
Dr Mary Harding, MRCGP

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