Blisters in the mouth that do not hurt or itch can be caused by external injuries, mucus cysts, oral herpes and other reasons. 1. External damage: due to bite wounds, food stimulation, such as eating too hard, too hot food, can cause damage in the oral cavity, blistering in the mouth does not hurt and itchy phenomenon. 2. Mucous cysts: due to salivary gland duct damage, so that saliva can not be normally secreted, thus forming mucous cysts, may appear in the mouth blistering painless and itchy phenomenon. 3. Oral herpes: Due to the infection of herpes virus, white blisters may grow in the mouth that do not hurt or itch, and if the herpes ruptures, pain may occur. When patients have blisters in the mouth that do not hurt or itch, it is recommended that they seek medical attention in a timely manner to be diagnosed by a professional doctor and given reasonable treatment.