The vast majority of adults will have mild bad breath when they get up from bed, mainly because if the patient usually has gingivitis or periodontitis, the bad breath is usually more serious, and after a night’s sleep the bad breath will be more serious. If there is no obvious bad breath, but only bad breath in the morning when you wake up, consider that it may be caused by a simple increase in oral bacteria. This is mainly due to the fact that the oral cavity is not a completely sterile environment, but a bacterial environment. Under normal circumstances, there are very many bacteria in the mouth, and the function of not chewing, talking and swallowing overnight makes the bacteria in the mouth doubly proliferate, multiply, and produce secretions. In the morning when you wake up, the bacteria inside the mouth and the secretions will produce a relatively large odor, and smell slightly bad breath.