Why do people get bad breath in the morning? The oral cavity is a highly non-sterile environment with a huge amount of bacteria. Throughout the day, a person takes in food, liquids, and produces large amounts of saliva. All of this washes away a significant portion of the bacteria and their waste products. Therefore, during the daytime, the breath is weak and almost imperceptible. At night, the amount of saliva produced drops dramatically. The bacteria feel great - they are warm, quiet, plenty of food in the crevices between the teeth, nothing to keep them from multiplying and carrying out their activities. In the process, they produce their own waste products, many of which have an unpleasant odor. That's what we smell in the morning.