If you think that poor oral hygiene causes bad breath, you’re right, but maybe not for the same reason that you may have thought. If you don’t brush and floss your teeth enough, bacteria can build up in your mouth. It’s that bacteria that causes bad breath. Better oral hygiene can help. But it’s important to remember that saliva works to flush away bacteria, so if you have a dry mouth, chances are you’ll experience bad breath. Here are some conditions that can contribute to the situation.
• Tooth and gum infections: Bacteria in the mouth that is there as the result of tooth or gum infections can cause bad breath.
• Breathing through your mouth: If you routinely breathe through your mouth for whatever reason, you probably have a dry mouth. That can cause bad breath.
• Medications: Many medications cause a dry mouth, which in turn can lead to bad breath.
• The common cold: If you experience a cold or any other form of respiratory tract infection, you could be breathing through your mouth or taking medications that lead to a dry mouth, both of which can mean bad breath.
• Diet: If you eat a diet that’s very high in protein and/or dairy products, you could be building up a large amount of amino acids in your mouth, and bacteria love amino acids!
• Other illnesses: More serious illnesses, such as diabetes or kidney disease, can also cause bad breath.
• Alcohol or drugs: Heavy consumption of either alcohol or drugs can dry out your mouth, leading to bad breath.
Resource: http://health.usnews.com/health-news/articles/2008/12/02/8-surprising-causes-of-bad-breath