There are two main reasons for dry mouth and bitter mouth: 1. local problems in the mouth. 2. problems in the digestive system. Local problems of the mouth are mostly due to poor oral hygiene, people who do not brush and rinse their teeth carefully, as well as those who do not go to the hospital regularly for scaling. Such people will have a lot of bacteria, food residues and toxins in their mouths, which will cause bitter and dry mouth. Injuries or infections leading to salivary gland hypofunction, causing a decrease in saliva secretion, will also cause dry mouth and bitterness, commonly found in patients with dry mouth syndrome. Diseases of the digestive system are mainly diseases of the liver and biliary system. People suffering from cholecystitis, gallstones, bile reflux and other diseases can cause dry mouth and bitterness due to bile reflux and bile stagnation. Fire in the body can also cause dry mouth and bitterness, commonly caused by indigestion, food accumulation, or dry mouth and bitterness caused by stress, depression and anxiety.