The medical name for bad breath is halitosis. Food particles breaking down in and around your teeth can give off a bad odor. Particles that remain due to poor dental hygiene can cause a build up of bacteria, which release sulfur compounds that make your breath smell bad. If not removed, bacteria that attach themselves to tooth enamel can form a film called plaque. Plaque produces acid that eats away at tooth enamel; causing the holes we call cavities. Sinus problems that lead to increased production of mucus provide a breeding ground for bacteria that cause bad breath. Another cause of halitosis is bacterial infection of the tonsils, known as tonsillitis.