Mouth bitter reasons include the following: 1, low immunity, endocrine disorders, parotid, submandibular glands and other glands are damaged, can not secrete sufficient mucus, the lack of saliva lubrication of the oral mucosa, the surface of the extremely dry, the formation of chapped, dry, bitter symptoms; 2, suffering from lichen planus, lips, cheeks, tongue, and other mucous membranes at the emergence of white papules composed of dendritic, reticulate pattern, roughness of the mucosa, vesicles occur, together with the bitter sensation; 3, pemphigus, pemphigus-like diseases such as maculopapular diseases, the oral mucosa can form larger blisters, easily ruptured, together with the bitter sensation. The mucous membrane is rough, erosion occurs, resulting in bitterness; 3, the occurrence of pemphigus, pemphigoid and other herpetic diseases, the oral mucosa can form a larger blisters, easy to rupture, together with the surrounding normal mucous membrane and tear off, exposing bright red trauma; 4, the lack of the oral mucosa after the protective effect of the oral mucous membrane, there will be a sense of bitterness in the oral cavity.