Why do I still have bad breath even after brushing and flossing? One common cause of bad breath is not brushing the tongue, especially the back of the tongue which can harbor bacteria and food debris. Try using a tongue scraper or your toothbrush to clean your tongue every time you brush your teeth. Other causes of bad breath are gum disease, plaque under the gumline, or tartar that’s harboring bacteria and isn’t removed by brushing alone. What are some other common culprits?