Bacteria. The stink-creating kind mostly hang out on the tongue, happily churning out gases as they munch on food particles and substances broken down from saliva, and multiply at night, when the salivary glands slow down (hence morning breath). Some people harbor more species of malodorous bacteria than others do, which may be why certain individuals are especially halitosis-prone. This month, a study in the Journal of Medical Microbiology suggests that H. pylori, the same bug that is often responsible for stomach ulcers, can cause bad breath and gum disease if it finds a home in the mouth.
