Under normal circumstances, there is no abnormal odor when the human body exhales, but when suffering from certain systemic diseases or oral local diseases, etc., the exhalation often has bad breath or exhales a special odor. There are many diseases that cause bad breath, but a general overview includes those caused by systemic diseases, oral diseases, consumption of special foods, and medications. Halitosis caused by systemic diseases is not common. Such as digestive system diseases caused by halitosis, due to food in the stomach for too long and fermentation, can be in the speech, exhale a sour smell or fecal odor emitted, and a large amount of foul sputum cough. With diseases of the nasopharynx, there can be an odor of rotting flesh when exhaling and speaking. Those who suffer from severe diabetes have an ammonia odor in their exhalation; patients with certain acute infectious diseases often have a sour odor exhaled from their mouth. When suffering from certain blood system diseases, the exhalation is often a fishy odor. In addition, some female patients, during menstruation or before menstruation, the breath exhaled from the mouth often has a bloody odor. Oral diseases cause bad breath is more common. From clinical observation, patients who come to the clinic for treatment of bad breath, almost 80% to 90% of them are led by oral diseases. The most common oral diseases are gum class (gum bleeding), periodontitis, exhaled gas for the strong odor; wisdom teeth pericoronitis, remnant crown, remnant roots, bad restorations, etc., have a heavy smell of corruption. In addition, poor oral hygiene, is also a common cause of bad breath. Taking different medications and eating certain strong-smelling foods. There are also different odors in the mouth, such as eating garlic, onions, leeks, shallots, exhaling a stronger garlic odor in the mouth; such as lead poisoning, there is a metallic taste in the mouth; cyanide poisoning, there is an almond taste in the mouth; excessive smoking and drinking people, there is a strong smell of alcohol and tobacco in the mouth, etc.