You should not pierce a blister on your mouth by yourself. It is best to go to the hospital and have a specialist see you. The most common type of blister on the lips is herpes labialis caused by herpes simplex virus infection, or mucus gland cyst. Herpes labialis occurs when clusters of small blisters begin to appear on the red edge of the lips, slowly breaking into patches and oozing crusts. These blisters contain the herpes simplex virus which is contagious, especially in children, and these fluids will also form new blisters on the skin if they flow onto the skin. Blisters on the lower lip can also be mucus gland cysts. Mucous cysts occur under the mucous membrane of the lip, often the size of a soybean, with clear edges, in the form of small transparent vesicles, painless. Most of them have a history of local bites. After puncturing by itself, a mucous fluid will flow out and the blisters temporarily disappear, but the rupture quickly heals and the mucous cyst reappears. And it is easy to recur, the cysts will appear with obvious discomfort, sometimes small cysts can disappear on their own, if the mucous cysts recur after their own puncture, they can not disappear on their own, they need to be completely removed by surgery, of course, there are many mucous cysts punctured also need to be surgically removed. So you can’t pierce a blister on your mouth by yourself. It is best to go to the hospital and ask a specialist for treatment.