› diseases-conditions › badBad breath - Symptoms and causes - Mayo Clinic Mar 10, 2018 · If you don't brush and floss daily, food particles remain in your mouth, causing bad breath. A colorless, sticky film of bacteria (plaque) forms on your teeth. If not brushed away, plaque can irritate your gums and eventually form plaque-filled pockets between your teeth and gums (periodontitis). Your tongue also can trap bacteria that produce ...