Like the reason behind a pesky cough or case of the sniffles, chronic oral halitosis, or bad breath coming from the mouth, is caused by bacteria. The average person has around 800 types of bacteria hanging out in his or her mouth [source: Haraszthy et al]. If you magnified a single cell from the surface of your tongue, you might see as many as 100 types of bacteria clinging to it [source: Yaegaki and Coil].
The mouth is like a bacteria factory, prepped with the ideal conditions for organisms to live and breed. You can compare the environment inside of your mouth to a sauna. In the same way those hot, humid rooms stimulate our bodies to pour out buckets of sweat, our clammy oral cavities encourage bacteria production. But it isn't the bacteria alone that turn our breath sour; rather, it's the interaction between the food we eat and that oral bacteria that sets off the chain reaction that ends with you frantically popping a peppermint.
Certain bacteria promote bad breath by first breaking down leftover proteins from food particles, dead cells and mucous into amino acids. In order to extract energy from those amino acids, the bacteria further dissect those molecules, causing them to release volatile sulfuric gases. Sulfuric gases give off that distinct rotten egg stench often added to natural gas lines to allow us to sniff out leaks. These bacteria thrive most abundantly in tucked-away areas of our mouths, including crevices between teeth and the back of our tongues.
Dry mouth also promotes halitosis. Our saliva actually serves as a natural mouthwash to get rid of those excess food particles and rinse away bacteria. When we sleep, our body slows saliva production, which explains the why we wake up with the oral stink bomb of morning breath -- and people with chronic dry mouth, or xerostomia, have even more pungent morning breath than most of us. Your medication could be prompting halitosis as well. Antidepressants, painkillers and antihistamines often include dry mouth as a side effect [source: Haraszthy et al].
Although oral bacteria initiate 85 percent of halitosis cases, foul breath may be a sign of problems elsewhere in the body [source: Merck]. When you get a sinus infection or a severe cold, your breath takes a turn for the worse as mucous production spikes and it leaks down the back of your throat onto your tongue. Gastrointestinal malfunctions, kidney problems and lung infection are also known to taint the breath. Lack of food can also have a malodorous effect: When your body runs out of sugar to burn for energy, it starts metabolizing fat, a process called ketoacidosis. And when the body burns the ketones in fat, it gives you fruity-scented breath [source: Mayo Clinic].
Now that we know what's behind halitosis, how might you nip it in the bud?