Most bad breath is produced by bacteria growing on the back of the tongue and upper throat. It can also be caused by medical conditions. Infections of the nasal passages and disturbances of metabolism such as diabetes, kidney and liver disease can all affect breath. The cause and treatment of bad breath overlaps both dentistry and medicine.

Most people who have bad breath, or think they have, try to treat it themselves. Self-help in the form of mouth rinses, breath fresheners, or a tongue scraper, along with regular dental visits for teeth cleaning often works. A few people have chronic bad breath no matter what they try. Others only think they have bad breath.

Ancient people in the Middle East, China and Europe left behind various forms of toothpicks. Sometimes, these were part of a set of personal cleaning items made from precious materials. From these artifacts, we learned that people have always worried about bad breath. The toothpicks were probably intended to remove bits of food stuck between teeth. Bits of food do start to smell if left in the teeth – and most likely the toothpicks solved the problem. We can still use this strategy today.

The famous Greek doctor Hippocrates described toothpowders and mouth rinses 2500 years ago. His own mouth rinse formula came from India. The medieval herbalist Hildegaard von Bingen described using fennel as a breath sweetener. Other natural remedies for bad breath include peppermint, parsley leaves and cardamon seeds. Still, focusing too much on bad breath can lead to unnecessary social isolation. Everyone has a bit of bad breath sometimes.

Causes of bad breath

Causes of Bad Breath

in children and youth

in adults

in the elderly

Metabolic diseases, such as diabetes or other changes in metabolism
Hiatus hernia
Something stuck in the nose or sinuses
Untreated decayed teeth in the mouth
Oral infection
Smoking

To avoid too much anxiety, be gentle in approaching the subject with children.

Periodontitis – gum disease
Poor oral health including lots of broken down or infected teeth
Hiatus hernia
Smoking, alcohol and dehydration
Coffee
Infection of the gums
Metabolic diseases and other medical conditions
Dry mouth (xerostomia), including a dry mouth caused by medication

Poor denture hygiene can involve amines
Dry mouth, which can be caused by medication
Metabolic diseases and other medical conditions
Hiatus hernia

One of the main causes of bad breath is the production of volatile sulphur compounds (VSCs) by bacteria that grow naturally in the mouth. The bad odour of rotten eggs comes from VSCs bacteria produce when digesting proteins in the egg. The same bacterial process happening on the tongue causes bad breath in our mouths. For some reason, human noses are sensitive to VSC at such low concentrations that they are measured as parts per billion. Our noses can clearly detect breath containing no more than 200 to 300 parts per billion of VSC. Natural amines produced by bacteria breaking down amino acids in the mouth also cause breath odours. The names of these amines – cadaverine and putrescine – indicate their foul smell. However, the nose cannot detect these amines with nearly the same sensitivity as VSC.

So-called ‘morning breath’ consists largely of VSCs on the tongue. Bacteria grow well overnight, as saliva flows very slowly during sleep. This dries out the back of the tongue, encouraging VSC production. Since the area is not flushed out by saliva, the odour becomes more noticeable. Control the smell by staying hydrated and cleaning your teeth and mouth well first thing in the morning. Remember to brush or scrape the back of your tongue as far back as you can manage, but do not overdo this.

A few people have breath odour most of the time. A minority are healthy and have healthy mouths. In people with persistent bad breath, there seems to be an imbalance in growth of oral bacteria. More bacteria associated with VSC production appear. We do not know how or why this imbalance occurs. Research has tried to identify molecules in saliva that might be different in these people. Part of treatment encourages the growth of normal bacteria in the mouth. Such treatment does not involve simply overcoming or ‘knocking out’ oral bacteria, because sometimes that approach causes bad breath.

In fact, in New Zealand, normal oral bacteria in the form of a strain of Streptoccus salivarius were developed as a probiotic treatment for bad breath. Other such probiotic treatments are underway, but all are still in the clinical trial stage. Simple remedies can involve gentle suppression of anaerobic bacteria in the mouth – the ones most closely associated with bad breath. Other remedies involve trying to bind VSCs in the saliva, so they do not come out of the mouth in air. All breath remedies on the market use either or both approaches to managing bad breath. Using a remedy like peppermint can also cover bad breath for a while.

Thanks to all the research in this area, we know more about why people get bad breath. One group of people likely to have bad breath are those with active or extensive gum disease (periodontitis). Bacteria associated with poor gum health produce VSCs. These bacteria also grow on the back of the tongue. One form of gum disease produces an odour generally described as ‘metallic.’ This condition is called acute ulcerative gingivitis and is usually associated with painful gums. People with inflamed tonsils may also have breath odour that contains lots of VSCs.

The condition of the esophagus, the tube from the throat to the stomach, can affect breath. In people who have a hiatus hernia, the esophagus stays slightly open. Stomach odour may scent the breath, especially if the person is hungry. Drinking coffee or smoking can make breath worse, since coffee stimulates stomach secretions and smoking dries the mouth. Some people taking antibiotics find stomach odour increases and then eventually goes away. Others have bad breath because of a sinus infection or even a chronic chest infection.

A range of metabolic diseases can produce breath odour. Poor diabetes control creates a smell like nail polish remover. Liver diseases and kidney disease are also associated with breath odour. In a few people, choline (found in eggs) transforms into a chemical that can contribute to a fishy odour of the breath and urine. There is a whole range of reasons why somebody can have bad breath. Many fall outside of dentistry and in the area of medicine.

What can you do?

What to do about bad breath

Practice good oral hygiene. Brush after meals and before bed. Floss once a day and scrape your tongue once or twice a day. Rinse your mouth with water if you are unable to brush.
Chew sugarless gum or try a mouth rinse.
Drink plenty of water.
Cut down on alcohol and coffee.
Eat a small cracker when hungry.
Have a dental check-up and cleaning. Discuss your concerns with your dentist, who may have products for you to try.
At your medical check-up, tell your doctor that you are worried about your breath.
Recruit a close friend to help find out what works to control your bad breath.
If you are concerned about bad breath, get help from a sympathetic person. Not everyone who thinks they have bad breath actually does. Halimetry can help set your thoughts at ease.
If you continue to have problems, a specialist in oral medicine at a dental school or clinic may be able to help.

Worrying about breath odour can be very socially isolating. It is almost impossible to detect and monitor your own breath. There is a remedy – find somebody to advise you. The human nose is still the most sensitive instrument we have to measure bad breath. Using the sense of smell in bad breath research is disguised under the term ‘neuroleptic assessment.’ If you are concerned about your breath, recruit a trusted friend who can tell you what works in controlling bad breath and what does not. The right person to work is often the person who tells you that your breath is bad. This person can also give support if you are unnecessarily afraid of having bad breath. If someone you know has breath odour, you might gently offer your help.

A number of instruments for measuring bad breath are used in the clinic. All can give clear proof to a patient and their caregiver of the presence or absence of levels of VSCs associated with bad breath. Appropriate treatment can then be recommended. The gas chromatograph is an example. One type, the OralChroma™, specializes in measuring oral VSCs. Many people working in this area use a portable monitor to measure VSC growth in a process called halimetry. The Halimeter™ is a souped-up adaptation of an industrial safety monitor. Instead of detecting ‘sour gas,’ it measures VSCs in mouth air. Like all aspects of scientific measurement, using an instrument to detect and measure VSCs in mouth air requires training for correct interpretation of results.

Such instruments have both benefits and limitations. They can be influenced or even deceived by other molecules, such as alcohol (frequently found in mouth rinses) and flavouring agents in products like toothpaste. The instruments used in clinics cannot detect amines which are associated with bad breath in some people, especially the elderly. Most important, the only thing this equipment can do is confirm bad breath at the time of measurement.

If you are worried about your breath, the best solution is to find an advisor you trust. If the problem persists, your doctor or dentist may be able to help find a solution.

Bad Breath Biology in action