There are many reasons for clear blisters inside the lips, excluding blisters after burns, generally consider mucus gland cysts or herpes virus infection, which can be roughly judged by the symptoms, or you can go to the hospital dermatology department to clarify the cause through examination. 1, mucus gland cysts: generally prevalent in the lower lip, often caused by the development of oral ulcers or bites, after the injury of submucosal glands, the lower lip mucus gland ducts will atrophy, bending, mucus excretion difficulties, the gland secretion blockage to form cysts, there will be translucent vesicles of soybean size. Mucus excretion difficulties, the gland secretion blockage after the formation of cysts, there will be a soybean-sized translucent vesicles, generally soft and elastic texture; 2, herpes virus infection: when the patient resistance is low, easy to induce herpes simplex virus infection, generally manifested as lip skin elevated, hemispherical, transparent blisters, pain is obvious, single or clusters appear.