According to WebMD, the causes of blisters or ulcers on the tongue are not always known, but they can be due to stress or injury. Other causes include a sharp tooth or ill-fitting dental appliances.
Mouth ulcers may develop as a result of a deficiency such as of vitamin B12, iron, folic acid or zinc. A person with an impaired immune system or who suffers from gastrointestinal diseases like Crohn's disease and celiac disease can get ulcers on the tongue as well as the on the inner cheeks, lips and on the roof of the mouth. Reactions to certain drugs may have the same effect.
Triggers that may cause mouth ulcers to arise include acidic and spicy foods, gum chewing and using a hard-bristle toothbrush. Daily flossing helps keeps bacteria at bay that may aggravate mouth ulcers.
Painful mouth ulcers usually respond well to over-the-counter mouthwashes, lozenges and gels, or even a salt-water mouthwash, but there is no cure for them, and they may reoccur periodically. If a mouth ulcer does not respond to treatment, is spreading or has become large or is still there after three weeks, sufferers should consult with a physician or dentist, who will often prescribe a mouth rinse or ointment.