Blue tongue may be caused by dietary factors, trauma, tongue hemangioma and other reasons. 1. Dietary factors: If the tongue is only blue and there is no other discomfort, the tongue may be blue due to eating some food containing green color. 2. Trauma: If the tongue is bitten or burned, localized bruising may occur. 3. Tongue hemangioma: poor blood circulation of the tongue as a whole can lead to localized or overall blue tongue. If the blue part of the tongue is accompanied by a slight bulge and blood vessels can be seen locally, it may be a symptom of localized hemangioma of the tongue. In addition to the above reasons, there may be thin mucous membrane of tongue abdomen, coronary heart disease, diabetes mellitus and other causes of blue tongue. After excluding non-physiological factors, patients should go to regular hospitals in time to find out the cause of the disease and take targeted treatment measures under the guidance of professional doctors.