Q My sister is in her late 40s. She suffers from bad breath, especially after she drinks coffee or eats fish. She feels very embarrassed, is constantly brushing her teeth and uses mouthwash but these do not seem to work. Can baking soda cure halitosis?

A The cause of bad breath in most people is anaerobic bacteria that reside at the back of the tongue, throat and gums. These bacteria, which grow best in environments devoid of oxygen, break down proteins and release odorous volatile sulphur compounds.

Diets high in protein such as fish, meat and dairy products can therefore worsen a person's breath especially in the presence of periodontal (gum) disease. Periodontal disease is brought about by dental plaque, the film of bacteria that constantly forms on teeth. The older a person gets, the more likely his or her bad breath is related to gum problems.

Another common cause of bad breath is dry mouth (xerostomia), which occurs when salivary flow decreases. With age, a person's salivary glands tend to work less efficiently and the composition and consistency of saliva changes. Saliva helps to kill bacteria and removes particles that may cause odour.

Dry mouth can also be caused by certain medications, medical conditions, breathing through the mouth, stress, alcohol as well as coffee. Besides coffee's lingering odour on our breaths, drinking coffee throughout the day may cause dehydration, resulting in dry mouth.

Other causes of bad breath include smoking, dieting, nasal/sinus infections, acid reflux from the stomach, hormonal factors and foods such as onions, garlic and cauliflower. The effects of odorous foods are, fortunately, short-lived.

The treatment of bad breath depends largely on the underlying causes. As it is caused by many factors, there is usually no one single treatment. A visit to the dentist is probably the best place to start. Regular professional cleaning and maintaining good oral hygiene are important for reducing the bacteria load.

Some special mouthwashes may also be effective. Baking soda may be useful for managing bad breath as it can change the level of acidity in a person's mouth, creating an environment that is not conducive for anaerobic bacteria.

Associate Professor Adrian Yap

Prof Adrian Yap is a consultant prosthodontist and dental director at Raffles Hospital

This article was first published in Mind Your Body, The Straits Times.