Bad breath can be caused by what you eat, not cleaning your mouth, dry mouth, smoking or other medical conditions. Persistent bad breath can also be one of the warning signs of gum disease. Brushing twice a day and flossing daily are essential to reducing bad breath and preventing gum disease. Brushing your tongue can help too. If you’re concerned about what’s causing your bad breath, see your dentist. They can determine the cause and treatment plan.