There are many causes of bad breath, also called halitosis. Your mouth may be the source. The breakdown of food particles and other debris by bacteria in and around your teeth can cause a foul odour. If your mouth becomes dry, such as during sleep or after smoking, dead cells can accumulate and decompose on your tongue, gums and cheeks, causing odour. Eating foods containing oils with strong odour such as onions and garlic, can lead to bad breath.
Foul-smelling breath also may be a symptom of illness, such as lung disease, diabetes or liver failure.

To reduce or prevent bad breath:
* Brush your teeth after you eat. Keep a toothbrush at work to use after eating. Brush using a fluoride-containing toothpaste at least twice a day, especially after meals. Toothpaste with antibacterial properties has been shown to reduce bad breath odours.
* Floss at least once a day. Proper flossing removes food particles and plaque from between your teeth, helping to control bad breath.
* Brush your tongue. Your tongue harbours bacteria, so carefully brushing it may reduce odours. People who have a coated tongue from a significant overgrowth of bacteria (from smoking or dry mouth, for example) may benefit from using a tongue scraper. Or use a toothbrush that has a built-in tongue cleaner.
* Clean dentures or dental appliances. If you wear a bridge or a denture, clean it thoroughly at least once a day or as directed by your dentist. If you have a dental retainer or mouth-guard, clean it each time before you put it in your mouth. Your dentist can recommend the best cleaning product.
* Drink plenty of water to avoid dry mouth. To keep your mouth moist, avoid tobacco and drink plenty of water – not coffee, soft drinks or alcohol, which can lead to a drier mouth. Chew gum or suck on candy (preferably sugarless) to stimulate saliva. For chronic dry mouth, your dentist or physician may prescribe an artificial saliva preparation or an oral medication that stimulates the flow of saliva.
* Adjust your diet. Avoid foods such as onions and garlic that can cause bad breath. Eating a lot of sugary foods also is linked with bad breath.
* Regularly get a new toothbrush. Change your toothbrush when it becomes frayed – about every three to four months, and choose a soft-bristled toothbrush.
* Schedule regular dental checkups. See your dentist regularly – generally twice a year – to have your teeth or dentures examined and cleaned.
* Chew fresh parsley. Chewing parsley may improve bad breath temporarily.