1. Unwelcome guests: The No. 1 cause of halitosis, bad breath, is oral bacteria. They often congregate on the deep surfaces of the tongue, produce a waste that is rich in sulfur compounds and create a dreadful rotten-egg smell. “Halitosis rarely comes from the digestive system,” says Dr. Ewaldo Wendler, a Miami dentist. “The cause is found in the mouth 90 percent of the time.”

2. The usual suspects: The most common dental causes of bad breath include dry mouth, gum disease, extensive dental decay, oral infections and abscesses, oral cancers, poor oral hygiene and a proliferation of specific types of teria. Medical causes include tonsillar infections, post nasal drainage, sinus infections, diabetes and lung diseases.

3. A closer look: Chronic dry mouth is the main culprit, Wendler says, because saliva washes away excess sulfur compounds and provides oxygen to the oral environment, thus preventing the proliferation of anaerobic bacteria. Certain prescription medications, alcohol and high quantities of coffee may induce or worsen a dry mouth, he says. High-protein foods, such as dairy products and fish, besides being trapped in the back of the tongue, can get lodged between teeth and cause bad breath.

4. Washed away: A tongue scraper and mouthwashes containing chlorine dioxide or sodium chlorite are crucial, Wendler advises. Used together, they will reduce the amount of anaerobic bacteria and neutralize the sulfuric compounds that create the bad breath.

5. Prevention: Brush and floss daily; drink more water; avoid mouthwashes with high concentrations of alcohol; chew sugarless gum to ease dry-mouth symptoms; cut down on coffee and odor-producing foods; quit smoking; and visit your dentist regularly. If the problem persists, get a medical evaluation.