A mucous cyst, also known as a mucocele, is a fluid-filled swelling that occurs on the lip or the mouth. The cyst develops when the mouth’s salivary glands become plugged with mucus.
A mucous cyst on the lip (or a mucocele on the lip) appears as a bump inside the lip. It is a fluid-filled lump that forms on the inner surface of the lower or upper lip, the inside of the cheek, or occasionally under the tongue, due to irritation or trauma.
The most common location to find a mucocele is the inner surface of the lower lip. It can also be found on the inner side of the cheek (known as the buccal mucosa), on the anterior ventral tongue, and the floor of the mouth.