What causes chronic bad breath, and what’s the best cure?

A. While everyone can expect some unpleasant odor after polishing off a meal laden with garlic or spices, bad breath from food should disappear within about 24 hours, once your body has fully processed the meal. When bad breath keeps returning, it’s usually because of lingering bacteria in the mouth, says James Hanley, periodontist and an associate dean at Tufts School of Dental Medicine.

The mouth is home to a complex mix of bacteria, which form communities on surfaces and in crevices of teeth, gums, and the tongue. The bacteria feed on particles of leftover food, and produce chemical byproducts that leave an odor. In 90 percent of cases of bad breath, the problem is because of food and bacteria that are allowed to collect in the mouth for too long. There is also some evidence that the specific type of bacteria living in a person’s mouth may also contribute to its smell. Over time, bacteria can form pockets of plaque between the teeth and gums, leading to periodontal disease; chronic bad breath can be an indicator of this disease process, Hanley says.

The simplest way to keep your breath fresh is to practice good oral hygiene, which includes brushing and flossing daily. Although many people find flossing time-consuming, Hanley says it’s the only way to clean out the spaces between teeth that brushing can’t reach. Most people also tend to skimp on brushing. Rather than brushing quickly several times a day, he says, “take the effort to thoroughly clean your mouth once a day,’’ flossing between teeth and making sure to brush all tooth surfaces and the tongue. Dental rinses can be an adjunct, but don’t rely on them; Hanley says it takes the physical force of brushing to remove more than a superficial layer of plaque.

See your dentist if good daily hygiene doesn’t seem to be enough to cure a malodorous mouth. A dentist can check for dental decay or periodontal disease. In about 10 percent of cases, bad breath is an indicator of a problem outside the mouth. If so, an ear, nose, and throat specialist can help identify the problem. Other sources of bad breath include infections in the sinuses, nasal cavity, or lungs; tonsil stones, small bits of bacteria and debris that form on the tonsils; or uncontrolled diabetes.

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