bad breath, or halitosis, is an unpleasant smell coming from the mouth. Halitosis can occur on occasion, or it can be a chronic condition. It may be caused by foods a person eats, poor oral hygiene, diseases, or other factors. The most common cause of bad breath is poor oral hygiene. 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. 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.
A lack of saliva can cause more bacteria than normal to build up in your mouth, as well as a change in the types of bacteria. A build-up of these in the mouth may lead to bad breath.
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.