A black blister on the tongue may be traumatic blood blisters, mostly caused by eating, bites, local irritants, etc., as follows. 1. Eating: too hard or too hot food may cause trauma to the tongue in the process of eating, also can be caused by swallowing too fast on the tongue caused by abrasion, this time the formation of blood blisters is generally larger. 2. Bite: accidentally biting the tongue can cause blood blisters on the tongue, blood blisters are generally small, can be accompanied by ulcers or erosion. 3. local irritation factors: oral stumps, stump crowns, bad restorations, etc. may produce friction on the tongue and blood blisters. There may be other reasons for a black blister on the tongue, it is recommended to go to the hospital in time, clear causes for targeted treatment.