More than 80 million people suffer from chronic halitosis, or bad breath. In most cases it originates from the gums and tongue. The odor is caused by wastes from bacteria in the mouth, the decay of food particles, other debris in your mouth and poor oral hygiene. The decay and debris produce a sulfur compound that causes the unpleasant odor. What causes bad breath? Bad breath is primarily caused by poor oral hygiene but can also be caused by retained food particles or gum disease. Does bad breath come from other sources than the mouth? Bad breath also may occur in people who have a medical infection, diabetes, kidney failure or a liver malfunction. Xerostomia (dry mouth) and tobacco also contribute to this problem. Cancer patients who undergo radiation therapy may experience dry mouth. Even stress, dieting, snoring, age and hormonal changes can have an effect on your breath. An odor that comes from the back of your tongue may indicate postnasal drip.