A blister in the mouth may be caused by the following reasons: first, bite wounds, bite wounds can easily cause blood blisters, can be used to cut, discharge pus and blood to promote its healing. Second, mucous gland cysts, mucous gland cysts can also be caused by the bad habit of lip biting. Third, hemangiomas, due to congenital vascular malformations, which are prone to produce purple blood blisters. Fourth, viruses, such as herpes simplex virus or hand, foot and mouth disease, may cause blisters in the mouth and require antiviral treatment. In the case of hand, foot and mouth disease, isolation is also required and appropriate use of antiviral drugs.