The common diseases that cause phlegm to be thick and sticky in the mouth include lung infection, fungal infection, bronchial dilatation and so on. 1. Combined lung infections: patients with combined lung infections can be accompanied by fever, fever will be a large amount of body energy consumption, but also consume body fluids, fever will be a large amount of sweating, loss of water, which will lead to phlegm, more viscous. 2. Fungal infections: the oral phlegm is thick and sticky also has a relationship with the type of infection of the pathogen, some patients due to fungal infections, which will lead to phlegm is sticky, can be filamentous, and it is often not easy to cough out. 3. Bronchial dilatation: Bronchial dilatation also occurs sputum thick and sticky, sputum volume can be more than a cup a day, and the nature of sticky. The sputum is white when there is no bacterial infection, and yellow or yellow-green when there is obvious bacterial infection. There are many causes of thick and sticky sputum, which need to be combined with the patient’s accompanying symptoms, and the cause of the disease should be clarified after completing the relevant examinations, so as to systematically treat the disease.