Updated 22 January 2018

Causes of bad breath

There are many risk factors and causes for bad breath; some common causes are listed below.

Around a quarter of chronic (i.e. of long duration) cases of halitosis are caused by odours coming from the lungs, alimentary tract, tonsils, adenoids etc. due to medical conditions.

These include kidney disease, diabetes, liver disease or the metabolism of certain types of drugs. Dieting may also result in halitosis.

The bacteria that produce the sulphide compounds thrive in dark, oxygen-poor environments like your gums and the back of your tongue where the taste buds are located.

These are shaped like tiny mushrooms and provide protective cover for about half the oral population of bacteria.

Other oral factors that can cause bad breath include

- Food impacted between teeth

- Fillings that are old and defective, broken or don't seal the cavity properly

- Diseases of the dental pulp

- Oral candidiasis

- Throat infections

- Soiled, unhygienic and ill-fitting false teeth. Some non-oral causes may include:

         - Diabetes

         - Kidney failure

         - Infections of the upper respiratory tract and sinuses

         - Nasal cancers

         - Lesions of the nose and back of the throat (nasopharynx)

         - Hiatus hernias

         - Contractions in the throat (oesophageal strictures)

         - Liver failure

         - Foods such as garlic and onions, which are rich sources of VSC.

Excessive dieting may also lead to bad breath, due to the increased metabolic breakdown of fats and proteins, and reduced chewing activity resulting in decreased salivary flow.

Postnasal drip is another non-oral factor that can cause halitosis. Mucus drains and coats the back of the tongue and throat, which is exactly where the bacteria live. Since mucus is made up of interlinked strands of protein, the bacteria thrive on breaking them down into odorous and sour-tasting sulphur-type compounds.

Reduced salivation or dry mouth can also be a common cause of bad breath. When your mouth is drier, you have less saliva and there is an increase in the alkalinity of the mouth.

Saliva contains oxygen, which keeps your mouth healthy and fresh. With less oxygen an anaerobic environment is created, perfect for bacteria to produce odorous and bitter compounds.

Some cases of dry mouth are naturally occurring, due to breathing for long periods through the mouth, for example, during sleep, or if lip closure is difficult due to improper "bite" of teeth (teeth don't fit properly and lips don't close spontaneously to form a lip-seal).

However, most cases of dry mouth are a side-effect of prescription medications (usually those for high blood pressure or depression), alcoholic beverages or mouthwashes containing alcohol.

Bacteria thrive on proteins and therefore the following high-protein foods can contribute to halitosis:

- Milk, cheese and most other dairy products

- Fish

In some people, bad breath is associated with gum disease. Your dentist can help prevent and treat gum diseases in various ways, depending on the type and extent of the problem, but your own daily home care can maintain gum health between appointments.

Cleaning the spaces between the teeth is of great importance.

One home tip for healthy gums (and fresher breath) is to smell the odour coming from the dental floss, and to work to clean those problem areas more carefully. 

Read more: 

Symptoms of bad breath 

Diagnosing bad breath 

Preventing bad breath 

Revised and reviewed by Professor Bill Evans, BDS Dip Orth(Witwatersrand). Orthodontist: South African Dental Association and Senior Specialist, Department of Orthodontics, University of the Witwatersrand, Johannesburg. February 2015.

Previously reviewed by Dr Jeff Michelson, South African Dental Association


Ask the Expert

Oral health expert

Dr Imraan Hoosen qualified from the Medical University of South Africa in 1997. Together with his partner, Dr Hoosen now runs a group of dental practices around Johannesburg (Lesedi Private Hospital, Highlands North Medical Centre , Brenthurst Clinic, Parklane Clinic, Simmonds Street Medical and Dental Centre, Soni Medical Centre- Newclare). Dr Hoosen can be contacted on 011 933 4096.

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