This is a very popular question.  Bad breath, also known as halitosis, is an unpleasant condition that is cause for social embarrassment.  Here are some causes:

• Eating foods with strong odors.  This is an obvious one, and examples are onions and garlic.  The good news is that bad breath from foods is temporary and should disappear once the food has been passed through your body.
• Poor oral hygiene.  Keep in mind that bacteria lives in your mouth and can be found in plaque or tartar.  When you do not brush or floss regularly, this odor-causing bacteria will continue to grow.  Bacteria also tends to accumulate on the tongue, so clean your tongue with your toothbrush or ask your dentist for a tongue scraper.
• Cavities & Abscesses.  Bacteria will release waste products in the form of sulfur compounds which will cause bad breath.
• Gum Disease.  In this case bad breath comes from having large amounts of bacteria in deep gum pockets in combination with bleeding gums
• Smoking.  Not only does smoking cause bad breath, it also stains your teeth, increases your risk to oral cancer, and irritates your gums.
• Dry mouth (xerostomia).  This could be due to salivary gland problems, certain medications, or chronic mouth-breathing.
• Medical conditions such as sinus infections that cause postnasal drip, diabetes, acid reflux, and liver problems can also cause bad breath.

How To Avoid It?

• Brush and floss regularly, and keep your tongue clean
• See your dentist regularly to ensure healthy gums and teeth
• Do not smoke
• Stay hydrated by drinking plenty of water
• Chew sugar free gum to help stimulate saliva flow

Thank you for reading. I encourage you to leave comments or questions below. To learn more about my practice, click on the link www.elitesacramentodentist.com

Your friendly dentist,
Dr. Sarah Po
Mar. 30, 2010

Source:  http://www.ada.org/public/topics/bad_breath.asp