Bad breath is common in daily life and can seriously affect the social and psychological state of the patient. What are the causes of bad breath? 1, some foods such as garlic, onion, leek, chives, coffee, etc. can cause bad breath. 2, gingivitis, periodontitis, pericoronitis, caries, chronic periapical inflammation and other oral diseases. 3.Plaque and calculus attached to the teeth. 4.The food embedded in the teeth and attached to the back of the tongue will ferment and emit an unpleasant odor. 5.Dry mouth syndrome can cause bad breath due to reduced saliva. 6, diseases in other parts of the jaw and face such as sinusitis, rhinitis, laryngitis, etc. can also cause bad breath. 7, certain systemic diseases such as diabetes, liver disease, kidney disease, bronchitis or infection of the lungs can also cause bad breath. 8, smoking can also cause a special cigarette odor. 9, the elderly due to reduced saliva production and cause bad breath. 10, some drugs such as certain sedatives, hypotensive drugs, atropine drugs, diuretics and Chinese medicine with warming effect. 11, indigestion, excessive stomach acid or long-term constipation, etc. can cause bad breath. Test method: lick the inside of the wrist with your tongue, if the smell is unpleasant, you can be sure that there is bad breath. Or the left and right palms together and closed into a bowl, wrapped around the mouth and nose, and then breathe into the gathered palms followed by nasal inhalation, you can smell how their mouth smells. If you find bad breath, it is best to go to a stomatologist first to eliminate the direct cause of bad breath – all kinds of oral diseases that may cause bad breath, and then check the whole body and treat them one by one. Brushing your teeth and chewing gum is the easiest way to prevent bad breath.