Bad breath occurs when sulfur compounds are produced in the body and released into the air. The most common source of this sulfur is anaerobic (without oxygen) bacteria that live in the grooves or fibers at the back of the tongue. These bacteria produce the sulfur that gives off an unpleasant smell. This frequently occurs when the mouth is dry, creating an ideal environment for anaerobic bacteria to thrive. Sulfur compounds are also produced when certain types of food are consumed. The compounds make their way into the bloodstream and then to the lungs, where they are excreted into the air we exhale.