Head down to your local grocery store, and chances are you'll find rows upon rows of mouthwash products, all of them making seemingly impossible claims about what they can do. Some of them take a page from the suntan lotion industry by offering "12-hour protection" from plaque and bacteria. Others say they'll make your teeth 50 percent stronger. Leaving aside all the marketing-speak, does using mouthwash actually make much of a difference? Or is our faith in what's become a $689 million-a-year industry simply the result of received wisdom?

Turns out it's a little bit of both. Our obsession with fresh breath has a history stretching back centuries, if not millennia. The ancient Chinese were known to rinse their mouths out using children's urine as a way to keep the gums clean. Ancient Greek scholars like Hippocrates and Pythagoras suggested solutions of salt, alum, and vinegar to maintain fresh breath.

In some places, getting rid of halitosis meant chewing natural substances instead of rinsing:

The Bible (Genesis) mentions labdanum (mastic), a resin that has been used in Mediterranean countries for breath freshening for thousands of years; it may be the original chewing gum. Other folk cures include parsley (Italy), cloves (Iraq), guava peels (Thailand), and eggshells (China). The Talmud suggests peppercorns.

With the Renaissance, people graduated to alcohol -- rinsing with wine or beer. Five hundred years later, alcohol remains a major ingredient in some of the leading brands of mouthwash. The original, gold-colored Listerine is reportedly 26.9 percent alcohol. And while alcohol-based rinses have been tentatively linked to higher rates of oral cancer, manufacturers aren't making it up when they say their products have been clinically proven.

Since the mid-1980s, six-month trials have repeatedly shown that using mouthwash actually has an appreciable effect on plaque and gingivitis, though to varying degrees. In one meta-analysis comparing prescription-strength and over-the-counter solutions, products like Listerine wound up reducing dental plaque in patients by between 13 percent and 56 percent, with a reduction in gingivitis of between 14 percent and 36 percent. Non-alcoholic rinses, such as Crest Pro-Health, had a 15 percent effect on plaque and gingivitis, respectively.

So does mouthwash really work? Unfortunately, the statistics are silent on the matter of bad breath -- which is the reason many of us probably use mouthwash in the first place. Still, what the manufacturers write on the bottle isn't all hype.