Small blisters inside the lips may be caused by burns, herpes stomatitis or salivary gland mucus cysts. 1. Scalding: If you drink water or food that is too hot on a daily basis, you may get scalded in your mouth, which may be manifested as small blisters and pain inside your lips. 2. herpes stomatitis: the cause is mostly herpes simplex virus induced, oral lesions can occur in any part of the oral mucosa, and if it occurs in the lips, it is often manifested as clusters of growing blisters. 3. Salivary gland mucous cysts: There are many salivary glands inside the lips, if they are bitten or the discharge channel is obstructed, salivary gland mucous cysts may appear, manifested as small blisters inside the lips. If there are small blisters inside the lips, it is recommended to consult a doctor in time and follow the doctor’s instructions for symptomatic treatment.