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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.
Home>Fresh Breath>Causes of Bad Breath>How Dry Mouth Leads to Bad Breath. Xerostomia, otherwise known as dry mouth, usually occurs when the production of saliva slows down. These barren conditions result in difficulty speaking, sore throat and the inability to find a glass of water large enough to quench the thirst. In persistent cases, it can also lead to bad breath.