Ever find yourself backing away from someone, discreetly covering your nose with anything at hand, and trying to scuttle away as quickly as possible? With bad breath affecting up to one in two people at some point in their lives, it's hard to escape from it.

"Bad breath is medically termed as halitosis and is described as an unpleasant, disagreeable and distinct odour," says Dr Koh Chu Guan, Senior Consultant at the Periodontic Unit, National Dental Centre Singapore (NDCS), a member of the SingHealth group.

A person with bad breath may not be aware of his condition as those around him might not want to hurt his feelings, or they might find it too awkward to tell him. To check for bad breath, try licking the back of your hand and let it dry before smelling it; or run dental floss between your teeth and sniff at it.

Most bad breath originates from bacteria in the mouth, found on the tongue surface and between teeth, for instance.

Causes of bad breath

Poor dental hygiene.  The most common cause of bad breath, food particles remaining in the mouth can collect bacteria and emit smelly hydrogen sulfide vapours. Bad breath can also happen with periodontal (gum) disease, which is gum irritation from plaque formation – a sticky, colourless film of bacteria on the teeth. It is estimated that about 80 per cent of Singaporeans suffer from gum disease.

Dry mouth (xerostomia).  Saliva helps to reduce odour by washing away food particles and bacteria. Dry mouth occurs when the saliva flow decreases due to reasons such as the use of certain medications, salivary gland problems and continuous breathing through the mouth. The slowing down of saliva production is also the reason behind funky 'morning breath'.

Food.  Besides remnant food particles in the mouth, certain drinks such as alcohol and coffee can cause a temporary odour. The types of food that we eat and later digest can lead to bad breath too. Examples include strong-tasting food like durian, onion, garlic and other spices. Once absorbed into the bloodstream, the oils get carried to the lungs to produce bad breath. It can take up to 72 hours before the smell goes away.

Medical.  Examples include discharge due to infections of the respiratory system, diabetes, metabolic disorders, kidney/liver failure and acid reflux. Certain medications may also cause bad breath.

Smoking.  Tobacco smoking dries out the mouth resulting in stale breath. The risk of gum disease also increases with smoking which can, again, lead to bad breath.

Dieting and fasting.  Low-carb diets lead to ketosis – the breakdown of fats for energy in the absence of carbohydrates. The release of ketones gives breath a fruity smell. When a person fasts, the digestive juices in the stomach can also cause odour. The salivary flow reduces too, causing dry mouth.

Read on for tips to treat and keep bad breath away.

Ref: T12