A blood blister in the mouth is most commonly caused by a bite to the mucous membrane, or too hard or too hot food that irritates the mucous membrane, causing submucosal bleeding. Since there is no wound on the mucosa, the bleeding cannot be discharged, so it is stored in the submucosa, so a blood blister is formed. In general, after the appearance of blood blisters, different treatment methods are chosen according to the size of the blisters. If it is a very small blood blister, usually do not need to deal with, drink more water, maintain good oral hygiene habits, do not eat too hard, too hot food continue to stimulate the affected area can be, the blood blister will be self-relieved. If the blood blisters are large, it is recommended to visit the stomatology department, after local sterilization, use a sterile syringe to draw out the blood from the blisters, and then compress to stop the bleeding. In addition, oral anti-inflammatory medication is needed to prevent the occurrence of infection.