What causes blistering in the mouth?

Blistering in the mouth can have several different causes. First, if you have injured those areas with hot food or by an accidental bite, then a small ulcer may form. Blistering in the mouth always raises the possibility that you have an oral herpes infection (also known as cold sores). These are caused by an infection of the herpes simplex virus. It can cause painful, sometimes burning ulcers that can come and go within and just outside the mouth. Most of the time, the immune system keeps the virus from activating, but during times of stress, it can break through. Sometimes these ulcers can form small blisters that pop, but can return. Other viral infections are possible as well. There are other less likely possibilities including Crohn's disease (which can effect the mouth as well as the colon) and Behcet's disease. While mouth sores can occur with these problems, they are usually not the primary complaint. I suggest that you first try and take a picture of the lesions so that if they go away, then you can still show a doctor. You should also schedule an appointment to see a primary care physician such as a family doctor. He or she can take a close look at your mouth and possibly determine the origin of these ulcers.