Bad breath also may occur in people who have a medical infection, gum disease, diabetes, kidney failure, or a liver malfunction. Cancer patients who undergo radiation therapy may experience dry mouth. Even stress, dieting, snoring, age and hormonal changes can have an effect on your breath. An odor that comes from the back of your tongue may indicate post-nasal drip. This is where the mucus secretion, which comes from the nose and moves down your throat, gets stuck on the tongue and causes an odor.
Bad breath originating in the stomach, however, is considered to be extremely rare.
Saliva is the key ingredient in your mouth that helps keep the odor under control because it helps wash away food particles and bacteria, the primary cause of bad breath. When you sleep, however, salivary glands slow down the production of saliva allowing the bacteria to grow inside the mouth. Morning mouth also is associated with hunger or fasting. Those who skip breakfast, beware because the odor may reappear even if you've brushed your teeth. Very spicy foods, such as onions and garlic, and coffee may be detected on a person's breath for up to 72 hours after digestion.