There are a number of possible causes of halitosis:
Poor oral hygiene
This is the most common cause. Bacteria that build up on your teeth – particularly between them – as well as your tongue and gums, can produce unpleasant-smelling gases. These bacteria are also responsible for gum disease and tooth decay.
Food and drink
Eating strongly flavoured foods, such as garlic, onions and spices, is likely to make your breath smell. Strong-smelling drinks, such as coffee and alcohol, can also cause bad breath.
Bad breath caused by food and drink is usually temporary. Good dental hygiene will also help.
Smoking
As well as making your breath smell, smoking stains your teeth, irritates your gums, and reduces your sense of taste.
It can also significantly affect the development of gum disease, another major cause of bad breath.
The most common cause of bad breath is poor oral hygiene, although other reasons are food and drink, smoking and certain medications and medical conditions (stock image)
Crash dieting
Crash dieting, fasting, and low-carbohydrate diets are another possible cause of bad breath. They cause the body to break down fat, which produces chemicals called ketones that can be smelled on your breath.
Medication
These include: nitrates – these are sometimes used to treat angina; some chemotherapy medication; and tranquillisers (phenothiazines).
If the medication you’re taking is causing bad breath, your GP may be able to recommend an alternative.
Medical conditions
In rare cases, bad breath can be caused by certain medical conditions. In dry mouth (xerostomia), the flow and composition of saliva may be affected.
Dry mouth can sometimes be caused by a problem in the salivary glands or by breathing through your mouth instead of your nose.
In some cases, gastrointestinal conditions can also cause bad breath. For example, a bacterial infection of the stomach lining and small intestine (H. pylori infection) and gastro-oesophageal reflux disease (GORD) have been linked to bad breath.
Other medical conditions that can cause bad breath include diabetes and lung, throat, or nose infections – for example, bronchiectasis, bronchitis, tonsillitis, and sinusitis.
Halitophobia
Some people are convinced they have bad breath when they don’t. This psychological condition is called halitophobia.
Source: NHS Choices