A black blood blister in the mouth instantly may be a submucosal hematoma of the oral cavity caused by local irritation or bite trauma. For example, eating too hot or rough food, or the mouth has a sharp tooth tip, etc., in the bite to stimulate the buccal mucous membrane in the mouth will instantly rise black blood blisters. If the blood blister is relatively small, no special treatment, self-absorption can be. If the blood blister is relatively large, it is best to puncture in time to facilitate the disappearance of blood blisters. In order to avoid the appearance of blood blisters in the mouth, do not eat too hot, too hard food, if there is a sharp tooth in the mouth, bite disorders should be corrected in a timely manner. Instant black blood blisters in the mouth, do not blindly self-treatment, so as not to cause infection. It is best to go to the hospital in time to avoid delays.