Diabetic patients usually have a typical ketonic breath (smell of rotten apple) that causes halitosis. These patients frequently show reduction in salivary flow and a high salivary viscosity which causes a reduction in its cleaning capacity and also a reduction in the action of salivary antimicrobials factors. These conditions facilitate the retention of exfoliated mucosa cells and the proliferation of microorganisms, especially on the tongue's surface. This bacteria mass that grows on the tongue surface is called tongue's coat. The most frequently found bacteria are anaerobic Gram negative that generally initiate its proliferation in the deepest interpapillary region where there is almost no oxygen.
When tongue's coat suffers contamination by anaerobic proteolytic microorganisms that produce odoriferous substances like volatile sulfide compounds (VSC), being sulfide hydrogen the most abundant, a smell of rotten egg can appear.