Mucus cyst

Alternative names:

mucocele; mucus retention cyst

Definition:

A transparent structure consisting of clear fluid trapped beneath a thin layer of mucus membrane.

Causes, incidence, and risk factors:

Mucus cysts are common on the inner surface of the lips and appear as a semitransparent fluid-filled blister. They are painless but bothersome because people are so aware of irregularities in the mouth. The cysts are thought to be caused by sucking action drawing the mucus membranes between the teeth. Mucus cysts are harmless. If left untreated, however, they can organize and form a permanent bump on the inner surface of the lip.