Black blood blisters on the edge of tongue may be caused by cavernous hemangioma or trauma, etc. The details are as follows. 1. Cavernous hemangioma: it is found in lips, tongue and bottom of mouth, and the superficial position can be dark colored lump, some hemangiomas are similar to blood blisters, but they are not as soft as blood blisters and easy to be broken. Some hemangiomas are similar to blood blisters, but not like blood blisters which are soft and easy to break. Hemangiomas often have positive signs of mobility test in low position. 2. Trauma: the sharp edges of residual roots and crowns and bad restorations, orthodontic arch wires, too hard and too hot food may cause trauma to the tongue to form blood blisters. Black blood blisters on the edge of the tongue may have other causes, it is recommended to go to the hospital in time, with the help of the doctor to clarify the cause of the targeted treatment.