Black petechiae on the tongue is a symptom of blood blisters, which is mainly caused by trauma or blood system diseases. 1. Trauma: If the tongue is subjected to external stimuli, such as too hot or sharp food, it will cause damage to the tongue mucosa; it will lead to submucosal hemorrhage and the formation of blood blisters, and the coagulation of blood in the blood blisters will make the tongue show the symptom of black petechiae. 2. Blood system diseases: leukemia, purpura and other blood diseases can cause bleeding under the skin and mucous membrane, so it will also lead to black bruises on the tongue mucous membrane. It is recommended to consult a doctor for a clear diagnosis of black bruises on the tongue and then treat the symptoms. Bruises caused by trauma can be left to heal on their own, while the above symptoms caused by blood system diseases should be treated by hematology specialists in a timely manner in order to prevent serious accidents from occurring in the organism.