The causes of blisters inside the lower lip are mainly eating factors, uneven teeth, mucus gland cysts, etc., as follows: First, eating factors: due to eating spicy and stimulating food, food with too high a temperature, or food with a hard texture, resulting in blisters on the lower lip, no special treatment is needed in this case, and most of them can be absorbed on their own. Second, uneven teeth: If there is an uneven alignment of the front teeth, or if there is a relatively sharp tooth tip, which can bite the mucous membrane of the lower lip, resulting in traumatic blisters, then the teeth need to be adjusted and treated. Third, mucus gland cyst: If the blisters on the inner side of the lower lip are light blue, translucent, and do not heal for a long time and cannot be absorbed on their own, it means that they are suffering from mucus gland cyst of the lower lip. It is due to the long-term bite trauma, resulting in the breakdown of the tiny mucus glands below the lips or the mucus ducts, resulting in the leakage and retention of the secreted mucus glands, thus causing mucus cysts, which need to be surgically removed in this case.