Bad breath at night is mainly due to the fact that the saliva secreted at night is itself less than during the day, plus improper cleaning leads to food debris remaining in the crevices of the teeth as well as the gum grooves, and bacterial growth is caused. It may also be caused by eating habits, gastrointestinal reasons, oral problems and so on. 1. Dietary habits: often drink alcohol, smoking, coffee, eating onions, leeks, garlic and other foods, or like to eat snail powder, stinky tofu and other smelly food, people are also prone to bad breath, this kind of bad breath can be improved by changing the dietary habits, no need to worry. 2. Gastrointestinal diseases: such as chronic gastritis, peptic ulcer, Helicobacter pylori infection, etc., there may be bad breath. 3. Oral problems: patients with gingivitis, dental caries, oral mucositis, periodontitis, periodontal disease and other oral problems, the mouth is prone to breeding bacteria, such as anaerobic bacteria, the bacterial decomposition of sulfur compounds, which produces bad breath. If the bad breath is caused by dietary problems can be improved by changing dietary habits and paying attention to the oral environment to make bad breath. If the bad breath is caused by gastrointestinal diseases or oral problems, you need to go to the hospital to clarify the cause of the disease and get treatment under the guidance of the doctor.