A lump on the lower lip is referred to as a mucocoele, mucocele or mucous cyst, which is caused by saliva escaping the surrounding tissue and forming a fluid-filled lump, notes DermNet NZ. In most instances, a mucocoele forms on the lower lip but can also appear inside the mouth.
This lump, or mucous cyst, can range in size from 1 to 15 millimeters in diameter. The color of the mucous cyst can range from light pink to blue, depending on the size, according to DermNet NZ. The reason for this color difference deals with the epithelium, or outer layer, of the lip and the capillaries in that specific area. Capillaries are small blood vessels that support the cardiovascular system, explains InnerBody.
There are numerous causes of mucous cysts. One of the most common relates to a person's habit of biting down on his lower lip. When doing so, a person's mucous duct becomes blocked, leading to swelling and expansion, states WebMD. In addition, a sudden blow to the mouth can also cause a mucous cyst. In most cases, the mucous cyst heals without treatment. However, if the condition persists, a person should see a doctor to discuss treatment solutions.