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1 Persistent bad breath or a bad taste in the mouth can also be one of the warning signs of gum disease; which is caused by plaque.  Dry mouth. This occurs when the flow of saliva decreases and can be caused by various medications, salivary gland problems or continuously breathing through the mouth.
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.he 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.