Sinus problems also contribute to bad breath. If you breathe through your mouth, it causes bad breath because the saliva dries up. That is a major cause of morning breath. I rinse with saline nasal spray every morning and at night. Gargle with equal parts warm water and peroxide. That will get the bacteria out of his throat. Use a tongue scraper and get as far back on the tongue as possible. Chewing gum helps because it makes you produce more saliva. If none of these things help, it may be a health issue and he should see a doctor.