Poor hygiene also contributes to bad breath when bacteria putrefy blood that oozes from periodontally diseased gum tissues, creating a particularly revolting and easily identifiable stench. Unclean dentures of any kind can cause bad breath in two ways, first by absorbing odor themselves and by helping to retain food particles.

Just as smelly substances are produced in stagnant water, offensive mouth odors result when the saliva becomes stagnant or diminishes . This is the basic cause of morning mouth, that noxious aroma that is observed upon wakening. During the night, salivary glands have slowed their functioning, and fresh saliva is meager, allowing the bacteria in the mouth to overgrow. Morning mouth tends to be most potent among those who snore or breathe through their mouths. Morning mouth disappears when you have rinsed your mouth or eaten something such as an apple or a slice of bread.

Morning mouth is also associated with hunger odor. This is a distinctive odor that accompanies the sensation of hunger. There is some evidence that hunger breath may arise from the putrefaction of pancreatic juices which pass into the stomach during the fasting state. Hunger breath is very apparent if the morning meal is omitted, even after tooth brushing.