Mucous cyst

Alternative names
Mucocele; Mucous retention cyst; Ranula (when on the floor of the mouth); Epulis (when on the gums)

A mucous cyst is a painless, bluish, transparent structure consisting of clear fluid trapped beneath a thin layer of mucous membrane.

Causes, incidence, and risk factors
Mucous 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 mucous membranes between the teeth. Mucous cysts are harmless. If left untreated, however, they can organize and form a permanent bump on the inner surface of the lip.


  • a transparent fluid filled bleb on the inside of the lip  
  • also seen on the tongue, palate, inside the cheeks (buccal mucosa) and the floor of the mouth (ranulas)  
  • lesion is painless

Signs and tests
Physical examination is sufficient to diagnose a mucous cyst.

A mucous cyst often can be left alone; it usually will rupture spontaneously. Opening the top of the bleb with sterile needle is curative. If the cyst recurs, it may need to be removed (excised).

Note: To prevent infection and damage to the tissue, opening the bleb should NOT be performed at home by the parents; it should be performed by your health care provider.

Expectations (prognosis)
Full recovery can be expected.

There are usually no complications.

Calling your health care provider
If it becomes uncomfortable, have the cyst examined by your health care provider during a routine examination.

There is no known prevention. Avoiding intentionally sucking the cheeks or lips between the teeth may be helpful.

Johns Hopkins patient information

Last revised: December 8, 2012
by Armen E. Martirosyan, M.D.

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