Bitterness at the base of the tongue may be caused by bad habits, or it may be a sign of liver and gallbladder diseases, papillitis of the tongue, burning mouth syndrome and so on. 1. Bad habits: overwork, overeating, lack of sleep and other bad habits can cause the tongue to become bitter. 2. Liver and gallbladder diseases: When cholecystitis, gallstones and other liver and gallbladder diseases occur, bile stagnation is abnormal and bile reflux can lead to bitter tongue. 3. Papillitis of the tongue: poor oral hygiene, lack of vitamins can lead to the occurrence of papillitis of the tongue, which can cause the dulling of the sense of taste, and can produce the symptoms of bitter mouth. 4. Burning Mouth Syndrome: When the small fiber nerves in the mouth or the central nervous system degenerate and damage, burning mouth syndrome will occur, causing the root of the tongue to be bitter. There may be other causes of bitter tongue, so please consult your doctor and follow his instructions.