There are three main causes of mouth blisters: First, it is a viral infection. There is a virus called herpes simplex virus, usually hidden in the ganglion behind the ear, when the resistance is low will come out and infect the lips with blisters. Second, is traumatic blistering, such as patients grinding to the lips, or eating too hot and too stimulating food, can also cause traumatic herpes of the lips. Third, the blisters are allergic blisters, because eating allergic food, when the blisters will be very large, and the whole symptom is exaggerated, but when the allergic food and drugs are stopped, the herpes will be quickly eliminated. These are the three causes of mouth blisters, and the treatment is basically the same, we should actively strengthen our own resistance, local can be through the wet compress way, or apply acyclovir ointment, to promote the healing of herpes.