Volatile sulfur compounds are thought to arise from the interaction of oral bacteria that occurs in conditions like gum disease and infections, and within pockets and crevices of your teeth. But your tongue is the real problem, according to a report in the Journal of Clinical Periodontology. Turns out, its large surface area—with all the tiny cracks and grooves—allow it to harbor lots of the microorganisms that lead to volatile sulfur compounds. In fact, in separate studies, scientists in Japan found that “tongue coating” had the greatest impact on producing volatile sulfur compounds in people’s mouths. This would also help explain why your breath is most likely to stink in the morning, since the compounds build up over night.