The causes of skin inside the mouth, mainly include the following: 1, when infected with herpes simplex virus, causing herpetic stomatitis, can appear in the lips and cheeks, tongue soft palate and other parts of the number of small blisters, broken to produce ulcers, accompanied by mucosal shedding. 2, allergic patients with allergies caused by the application of drugs and allergic stomatitis, the oral mucosa can produce erythema, blisters, etc., the wall of the blister and the surrounding tissue is easy to shed. 3, When suffering from exudative erythema multiforme, the oral mucosa forms blisters extensively, with large areas of erosion, accompanied by a large amount of exudate, forming a thicker pseudomembrane. 4. When oral mucosal diseases such as aspergillosis or aspergillosis occur, the mucosa will form a large volume of blisters, and the wall of the blisters will recede in all directions after breaking, and will easily fall off together with the surrounding normal mucosa.