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By A T McPhee
Current Science 4-5 Volume 88, Issue 6  (8 November 2002)

So I go, ‘What’d you do that for?’ And she goes, ‘I felt like it, duh.’ So I go-”

“Yo, dude.”


“Get a mint, man. I mean, your breath-it’s rancid.”

What? Me? Bad breath? After I heard that, I started popping mints like crazy. But then my doctor told me about this wicked research on halitosis. That’s bad breath. Like the fact that almost all bad breath starts in the mouth, not in the stomach. And that bad breath is caused by bacteria, not stuff like garlic.

Now I know some tricks to take the rankness out of my breath. I’m halitosis-free. Let me tell you, that’s hot.


The “dude” above isn’t real, but his situation is. Millions of teenagers and others tend to have less– than-sweet-smelling breath. In one recent study of college students in Brazil, researchers found that one in three students had at least one family member with bad breath.

Many people think odors from the stomach cause bad breath. Not true. A vast majority of cases are caused by odors coming from the back of the tongue. And what produces those odors? Bacteria that live in the mouth.

Those bacteria release several chemicals as they grow, including hydrogen sulfide (H2S), a colorless gas that smells like rotten eggs. H2S is commonly released by decaying matter, such as that found in sewers, barns, and the holds of cargo ships. Volcanoes also release H2S.

Other gases released by bacteria in the mouth include cadaverine, isovaleric acid, methyl mercaptan, putrescine, and skatole-all of which have a distinctly foul odor. Methyl mercaptan smells like rotting cabbage. Isovaleric acid smells like sweaty feet. Not exactly pleasant.


The bacteria responsible for producing such rank odors are anaerobic, meaning they can survive in an environment with little or no oxygen. Anaerobic bacteria thrive in the tiny nooks and crannies of the tongue, especially at the very back of the tongue. Not much oxygen reaches those spots.

As the bacteria grow, they feed on amino acids, chemicals that are the building blocks of proteins. The breakdown of amino acids releases H2S and other rancid chemicals. Eating foods high in proteins, such as meat, eggs, and fish, can leave behind enough amino acids in the mouth to feed an army of odor-causing anaerobes.

Those anaerobes also feast on proteins in secretions from the nose That’s why people with post-nasal drip often have halitosis. In a person with post-nasal drip, fluid from the nose continually streams down the back of the throat. Bacteria feed off this stream and release stinky H2S and other gases.


How can you tell whether you have bad breath? A device called a Halimeter® tests for the presence of H2S and other stinky gases. Many dentists use Halimeters to determine whether their patients have halitosis. Researchers at the University of Oviedo in Spain have been working on a new halitosis test. It uses a special light to measure how much H2S is present on mouth surfaces.

Test or no test, there are many ways to make sure your breath stays fresh all day. Here are a few:

  • Drink lots of fluids to flush the tongue and keep it clean. Fluids also help prevent mouth dryness, which promotes bacterial growth.
  • Rinse and gargle with a mouthwash before bed to reduce bacterial growth overnight.

  • Eat a healthful breakfast, to stimulate the flow of saliva, which helps keep the tongue clean.

  • Brush and floss your teeth at least once a day, preferably before bed.

  • Regularly and carefully scrape the back of your tongue with a plastic tongue cleaner. Gently scraping the tongue keeps bacteria from building up.

Remember, dude, to stay halitosis-free, forget the mints. Instead, flush, brush, and scrape your way to fresh breath.