Dry and bitter mouth may be caused by poor oral hygiene, salivary gland diseases, bad oral habits and so on. 1. Heavy dental calculus in the mouth may often stimulate intraoral bleeding, swollen gums, etc., when the intraoral flora imbalance, dry mouth and bitter mouth will occur. 2. Inflammation of salivary glands or tumors can affect salivary secretion, generally a decrease in salivary secretion, dryness of the mouth, long-term dryness of the mouth will affect the digestion of food in the mouth, easy to mouth bitter. 3. Frequent smoking, chewing betel nut, staying up late, eating stimulating foods may stimulate the mucous membrane in the mouth to appear white spots, lichen planus and other diseases, dry and bitter mouth and eating discomfort.