Poor Dental Hygiene
Bacteria breaks down food particles trapped in the teeth or mouth. The combination of the bacteria and decaying food in your mouth produces an unpleasant odor. Brushing and flossing regularly removes trapped food before it decays, but also removes plaque, a sticky substance that builds up on your teeth and causes odor. Plaque buildup can cause cavities and periodontal disease. Bad breath also can be a problem if you wear dentures and do not clean them every night.
Strong Foods and Beverages
When you eat onions, garlic, or other foods with strong odors, oils from the foods are absorbed into your stomach during digestion. These oils pass into your bloodstream, travel to your lungs, and are noticeable in your breath for up to 72 hours. Drinking beverages with strong odors, such as coffee, can contribute to bad breath.
Smoking cigarettes or cigars causes a bad odor and dries out your mouth, which can make odor even worse.
Dry mouth can occur if you do not make enough saliva. Saliva helps keep your mouth clean and reduces odor. Dry mouth can be a problem if you have a salivary gland condition, sleep with your mouth open, or take certain medications, including those that treat high blood pressure and urinary conditions.
Periodontal disease happens when plaque is not removed promptly from teeth. Over time, plaque hardens into tartar. Tartar cannot be removed by brushing and can irritate your gums. Tartar may cause pockets, or small openings, to form in the area between the teeth and gums. Food, bacteria, and dental plaque can collect in the pockets, causing a strong odor.
Sinus, Mouth, or Throat Conditions
Bad breath odor may develop if you have a sinus infection, postnasal drip, chronic bronchitis, or an infection in your upper or lower respiratory system. Tonsil stones also can be a source of bad breath because bacteria tend to collect on the stones.
Illnesses or Diseases
Unusual breath odor can be a symptom of some diseases, including kidney disease, diabetes, and gastroesophageal reflex disorder (GERD). If you have kidney or liver failure or diabetes, your breath may smell fishy. When your diabetes is not under control, your breath may smell fruity.