A blood blister on the tongue is called angina bullosa hemorrhagica, or ABH, and is the collection of blood under the skin of the tongue, according to Medscape. It is usually not associated with any other medical issues.
Once they burst, blood blisters on the tongue form ulcers that may be mistaken for more serious but rare conditions such as autoimmune disorders and other skin blistering disorders, dermatitis herpetiformis, or a low platelet count, according to Medscape. They can be painful when they are in the form of blisters but once they burst ABH are generally painless and clear up on their own within a week, according to an article on Pubmed from the School of Dentistry of the Catholic University of Rome, and do not leave scars. It is assumed that they are the result of some form of trauma that causes the capillaries to bleed beneath the skin, forming the blister, states Medscape.
According to oral surgeon John Doran, eating hot foods and dental and periodontal work, including injected anaesthetics, may be sources of trauma, and patients with ABH may complain of a burning or stinging pain just before the blisters erupt. ABH most often affects people middle aged and older, and family history does not appear to be a factor. There is no need to treat ABH, since they burst after a short time and heal on their own.