Sour and bitter mouth may be caused by poor oral hygiene conditions, such as a large amount of calculus and plaque around the gums, when the gums are prone to redness, swelling, soreness and pus, and dysbiosis of the oral flora is more likely to produce the phenomenon of sour and bitter mouth. It may also be due to inflammation of the tongue, which is caused by dysbiosis, or it may be due to a swelling of the tongue that produces a sour and bitter mouth. In addition, salivary gland diseases, such as tumors in the salivary glands and stones in the ducts of the salivary glands, can also cause low saliva production in the mouth. If there are gastrointestinal diseases or liver and gallbladder diseases, it can also lead to discomfort in the mouth. It is recommended that active examination and symptomatic treatment be carried out.