What causes, and how do I cure, chronic bad breath?

Not a big garlic eater or anything like that. Even after brushing teeth… breath really stinks after about five minutes.

Any ideas on the cause or cure?

Some of the oral bacteria that create the waste products that are responsible for causing bad breath live in the dental plaque that accumulates on and around a person's teeth, both at and below the gum line. A thorough brushing and flossing technique is needed in order to remove this plaque and also remove any food debris that is left in the person's mouth after eating that could be used as a food supply by these bacteria.
Most people overlook cleaning their tongue, however, starting to do so on a regular basis can be the single most beneficial treatment for bad breath (halitosis) that a person can institute.

The posterior portion of the tongue in comparison only rubs up against the palate (soft palate) relatively gently during tongue movements. This soft palate contact does not provide enough friction to produce any significant cleansing. For this reason it is typically the posterior aspect of the tongue that is found to harbor the bacteria that cause a person's bad breath, and thus the posterior tongue is the most important area to clean.
There are various methods you can use to clean the posterior portion of your tongue.
Your toothbrush or a specialized tongue brush can be used to clean your tongue. To do so, start as far back as possible and then make brush strokes outward, toward the front of your mouth. You need to use some pressure but of course not enough to cause irritation to your tongue.

If you allow yourself to become dehydrated your body will try to conserve moisture by reducing its production of saliva. Saliva has a cleansing and diluting effect on the bacteria and bacterial waste products that cause bad breath. A reduction in the amount of saliva in your mouth can make it harder for you to control odors associated with your breath.

Rinse your mouth with water often.
Stimulate your mouth's flow of saliva.
Clean your mouth well, especially after eating foods high in protein content.

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