What causes chronic bad breath?

Gums, teeth, food: If stomach problems or disease is not an issue, then bad breath is often caused by gum disease. Daily brushing and flossing, and regular dental cleanings would be the treatment. Other culprits are decayed teeth and wisdom tooth problems. Don't mask a bad breath problem. See a dentist for a proper diagnosis.

Gum disease for one : Tonsillar stones are one of the most common causes of chronic bad breath. Periodontal disease is another. Also a decayed tooth, or gastric reflux as well. Don't over use mouth rinses to hide oral odors, rather see a dentist or ENT to rule out some of these issues.