If blistering occurs under the tongue, two causes are considered, as follows: 1. Blisters caused by herpes simplex virus infection, if this is the case, the patient will usually have a fever and local discomfort before blistering. This is because of the fact that the patient has a lot of time to get the best out of the problem. 2. The blisters under the tongue are likely to be mucus cysts, or cysts in the sublingual or submaxillary glands. At this time, it is mainly a localized disease of the gland. If the blister does not rupture for a long time, or even if it becomes locally hard, it needs to be surgically removed. If rupture of the blister occurs within a short period of time and does not recur, there is usually no need for any disposition.