The causes of blisters on the inside of the mouth may include improper diet, irritation of the oral structures and viral infections. 1. Improper diet: Blisters may appear on the inside of the mouth due to the consumption of spicy and irritating foods, dry and hard foods, as well as foods that are too hot. Patients should change their bad dietary habits, avoid spicy and irritating foods, and try to eat mild foods. Drink plenty of water, keep the mouth area clean and dry, usually the blisters can subside on their own. 2. Incomplete oral structure: there are residual roots, crowns or sharp tips in the mouth, which may irritate the inner wall of the mouth by repeated friction during eating, and blisters may appear. The patient can suction the liquid inside the blister through the tip of a sterile needle, and at the same time, can follow the doctor’s instructions in the trauma of localized topical application of watermelon cream spray, tin-like powder or ice boron powder and so on. 3. Viral infections: viral infections such as herpes simplex virus infection can cause small blisters with pinpoint size on the inner wall of the mouth. This situation should be timely antiviral treatment, follow the doctor’s instructions to take drugs such as tenofovir, entecavir, ribavirin and so on. If the blisters on the inner wall of the mouth do not get better when you eat, you should go to the hospital in time to avoid delaying your condition. The application of drugs need to strictly follow the doctor’s instructions.