Bad breath is the annoying and unpleasant breath that comes out of the mouth. Halitosis arises from various acute and chronic diseases of the human body, it is not a disease in itself, but a disease sign. The main causes of bad breath are: ① oral diseases (dental caries, gingivitis, periodontitis, oral mucositis, etc.). ② gastrointestinal diseases (peptic ulcer, functional dyspepsia, etc.), smoking, drinking alcohol and often eat onions, garlic, leeks and other spicy stimulating food, or addicted to stinky tofu, rotten eggs and other food with a bad smell. ③ dieting to lose weight, or unable to eat due to illness, so that the secretion of saliva is reduced. ④Inadequate ovarian function in adolescent girls, when the level of sex hormones is low, the resistance of oral tissues decreases, making it easy to infect germs and thus produce bad breath. ⑤ Chemotherapy patients also produce strong bad breath. The prevention and treatment of halitosis is to pay attention to oral hygiene, forbidden to eat smelly food, in the treatment, first of all, to actively treat the original disease. The main methods to eliminate bad breath are 1. Maintain oral hygiene: brush your teeth at least twice a day with care, clean your tongue, and floss to remove meat and vegetable scraps from your teeth and remove dirt from your teeth. Get a new toothbrush every month to prevent the accumulation of bacteria on the toothbrush. Rinse your mouth with water after meals. Rinsing with water can remove some food residues left in the mouth and prevent bad breath. 2. Replenish water: dry mouth is easy to cause bad breath, and saliva has a natural bactericidal effect, it can also help remove food residues, help keep the mouth clean, so to fully hydrate. 3. Eat foods that can freshen your breath: eat more vegetables, because they contain a lot of fiber, which can help digestion and solve the problem of constipation. Foods that help destroy dental plaque can also be used to eliminate bad breath. 4. to develop a regular diet life: this is also an important factor to improve the immunity of the human body.