There are many reasons for thick and yellow tongue coating, which can be divided into physiological and pathological reasons, and pathological reasons mainly include digestive and respiratory diseases. 1. Physiological: If you have recently eaten pineapple and oranges and other foods with coloring, you will find that your tongue is thick and yellowish just after eating them; you will also have this symptom if you are under too much pressure, have an irregular diet, or don’t rinse your mouth and brush your teeth for a long time. These are normal physiological phenomena, no additional special treatment. 2. Pathological: diseases that cause thick and yellow tongue coating mainly include digestive diseases, such as indigestion, colitis, gallstones and cholecystitis, which affect the metabolism of the liver and lead to this symptom; respiratory diseases such as colds and flu can also lead to this symptom. If you suspect that this phenomenon is pathologic, it is recommended that you go to the hospital in time.