Bad breath stems from bacteria in our mouths that dissolve our food, preparing it for digestion and for use in the body. A side effect of this process is the emission of other compounds that can carry with them a particularly displeasing odor.
Most often bad breath will emanate from the tongue, as the warm moist texture is a perfect breeding ground for bacteria. However, the stomach and esophagus can also play a minor role as acids and gasses erupt upwards in the form of a burp or belch.
Combating bad breath can be easy, but not for everyone. Some people have chronic bad breath or halitosis. These people will have a difficult time getting rid of their bad breath, and may have to seek aid from a dental professional for extra help. For the rest of us, regular brushing, flossing, and mouthwash will be all that is necessary to keep our breath fresh and smelling clean.