This fear of foulness may help explain why Americans spend $1 billion a year on mouthwashes and other breath-freshening products. Most cases of bad breath result from bacteria that live in the mouth, according to William Replogle, Ph.D., professor of family medicine at the University of Mississippi Medical Center in Jackson. As these microbes feed on food residues, they produce foul-smelling compounds that make your breath offensive. They also produce irritating toxins that cause your gums to pull away from your teeth, forming pockets that harbor even more bacteria. And the more bacteria that live in your mouth, the worse your breath becomes.

In cases of chronic halitosis, the tongue may be an unwitting coconspiratorin this bacterial bacchanalia, according to research conducted by Walter Loesche, D.D.S., professor of dentistry and microbiology at the University of Michigan in Ann Arbor. He and his colleague Erika De Boever, D.D.S., found that the backs of some people's tongues have deep crevices where odor-producing bacteria thrive.

Bad breath tends to become more common with age. As you get older, you produce less saliva, which normally helps keep bacteria in check. For the same reason, you're more prone to this if you take drugs that dry your mouth, such as antihistamines, decongestants, and pain relievers.

Even morning mouth-the first-thing-in?the-morning kind of results from lack of saliva. When you sleep, you stop salivating, which allows bacteria to build up.

Ironically, most people who worry about it don't have it, according to Dr. Loesche. But how do you know if you do? Apparently, people will try just about any?thing to avoid the potential embarrassment of having to ask someone else. Unfortunately, the only surefire way to find out is to ask your spouse or a trustworthy friend to tell you the truth.

If you do have bad breath, you'll need to figure out how to bully those odor-producing bacteria into submission. That means good oral hygiene. Brush your teeth at least twice a day and floss at least once, advises Anne Simons, M.D. "Don't just wave the brush around your mouth," she says. "Brush thoroughly, especially around your gum lines. Floss thoroughly as well."