It depends on the location of the blisters. Nonetheless, Anbesol can be used to speed recovery time and numb the affected area(s.) You may want to do some research concerning cold sores and blisters or ulcers. Warm salt water rinses and diligent oral hygiene checks can prevent reoccurrence of any tears or sores concerning your mouth. Just to be safe, you should also wash your hands after making contact with the affected area(s) and discard & replace your toothbrush once the blister(s) have gone.
I have had them all my life and the only thing I use all the time now is Campho-Phenique you will find it at any store basically it will be in a yellow box with fast drying on it for cold sores. I live by it