''Halitosis rarely comes from the digestive system,'' says Ewaldo Wendler, a Miami dentist. ''The cause is found in the mouth 90 percent of the time.''

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 bacteria. Medical causes include tonsillar infections, post nasal drainage, sinus infections, diabetes and lung diseases.

A tongue scraper and mouthwashes containing chlorine dioxide or sodium chlorite, used together, will reduce the amount of anaerobic bacteria and neutralize the sulfuric compounds.

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.