Persistent bad breath or a bad taste in your mouth may be warning signs of gum (periodontal) disease. Gum disease is caused by the buildup of plaque on teeth. The bacteria cause toxins to form in the mouth, which irritate the gums. If gum disease continues untreated, it can damage the gums and jawbone.

Other dental causes of bad breath include poorly fitting dental appliances, yeast infections of the mouth, and dental cavities.

The medical condition dry mouth (also called xerostomia) can also cause bad breath. Saliva is necessary to moisten and cleanse the mouth by neutralizing acids produced by plaque and washing away dead cells that accumulate on the tongue, gums, and cheeks. If not removed, these cells decompose and can cause bad breath. Dry mouth may be caused by the side effects of various medications, salivary gland problems, or continuous breathing through the mouth.

Many other diseases and illnesses may cause bad breath. Here are some to be aware of: respiratory tract infections such as pneumonia or bronchitis, chronic sinus infections, postnasal drip, diabetes, chronic acid reflux, and liver or kidney problems.