Waking up in the morning to find white mucous membranes in the mouth may be caused by less saliva secretion, slower flow and coagulation, or it may be a Candida albicans infection. The accurate statement is not white mucous membrane, but the oral mucus in the sleep may be less secretion, discharge slower flow, water evaporation dried up due to. It is also not ruled out that there may be food debris in the mouth failed to clean up, and saliva mixed together, because there may be open-mouth breathing during sleep at night, the mixture dries up and adheres to the surface of the oral mucosa. This whiteness will disappear naturally after waking up through behaviors such as washing, drinking, and eating. There is also the possibility of a white pseudomembrane as a result of Candida albicans infection. In addition, there is another case where the mucous membrane of the buccal part of the mouth is tightly attached to the surface of the lateral teeth during sleep, and traces are left behind, and the whitish phenomenon of the mucous membrane is found after waking up, which can disappear naturally after opening the mouth and moving around. It is recommended to consult a doctor for timely examination and treatment of the white mucous membrane phenomenon in pathological conditions.