A black and purple blood blister on the inside of the mouth is considered to be a hemangioma in the mucosal area of the inside of the mouth if it persists for a long time. Patients can be examined by a specialist and may have to be treated by surgery or sclerotherapy after identification. In the case of blackish-purple blisters that appear for a short period of time, it is more common to see localized damage to the mucosa from eating or other causes, such as bites or burns, which can lead to the formation of blisters and blisters on the inner lining of the mucosa. If the blisters are small, they can usually be absorbed naturally and gradually subside. If it is large, you should go to a specialist and use a sterile syringe to aspirate the blisters, and then use some growth factor spray or other drugs to promote repair and healing, which can usually be healed in a short time.