When a swelling or “bubble” appears beneath the tongue, it can cause immediate concern due to the visible nature of the area. This sublingual region, or floor of the mouth, is home to a high concentration of structures, including the major sublingual salivary glands and numerous minor salivary glands. The area is highly vascularized, which is why swelling or bruising may appear prominent and sometimes bluish. While this anomaly is often alarming, the majority of causes are benign and directly related to a disruption in the normal flow of saliva. Understanding the mechanisms behind these fluid-filled sacs helps to demystify the symptom and guide the appropriate next steps.
Blocked Salivary Glands
The most frequent cause involves a problem with the salivary glands located in the floor of the mouth, which produce saliva that drains into the oral cavity through small tubes called ducts. If a duct becomes obstructed or damaged, the saliva cannot exit properly and instead leaks into the surrounding soft tissue, forming a fluid-filled sac.
The general term for these benign, mucus-filled swellings is a mucocele; when it occurs specifically on the floor of the mouth, it is called a ranula. Ranulas are typically associated with the major sublingual salivary gland and are often much larger than mucoceles found elsewhere in the mouth. The name “ranula” comes from the Latin word for frog, because the large, often translucent, bluish swelling can resemble a frog’s throat.
Ranulas form when the main duct of the sublingual gland is either injured or blocked, causing saliva to pool in the tissue above the mylohyoid muscle. They are categorized as a simple ranula, which remains in the floor of the mouth, or a plunging ranula, which extends downward into the neck. Blockage is often caused by trauma, such as accidental biting or injury, though sometimes the cause is not identified. The resulting collection is a smooth, soft, and usually painless dome-shaped swelling that may interfere with speech or swallowing if it grows large enough.
Common Physical Irritations
Not every lump or bubble under the tongue is a fluid-filled cyst; some may be the result of a physical injury or a common oral lesion. Accidental trauma to the delicate tissue on the floor of the mouth, such as scraping the area with sharp food or biting down, can cause temporary swelling or bruising. This localized injury can lead to a hematoma, a collection of blood outside of the blood vessels, which can appear as a dark, tender swelling that typically resolves as the body reabsorbs the blood.
Other common, non-glandular lesions may be mistaken for a bubble, although they present differently. Aphthous ulcers (canker sores) are painful, shallow sores that appear on the movable parts of the mouth, but they are generally open lesions rather than fluid-filled sacs. Similarly, a bony growth called a torus mandibularis can sometimes form on the lower jaw near the tongue, but it is a hard, slow-growing prominence. These physical irritations are usually self-limiting, disappearing on their own within a matter of days or a week as the tissue heals.
Immediate Steps and Professional Advice
If a bubble appears under the tongue, the first step is observation and gentle care, but there are certain actions to avoid. It is strongly advised not to attempt to pierce, drain, or “pop” the bubble at home. Doing so can introduce bacteria from the mouth into the deeper tissue, leading to a serious infection, or cause further damage to the salivary gland duct, which could worsen the condition. Most mucoceles and ranulas, especially smaller ones, can spontaneously rupture and resolve on their own as the body reabsorbs the fluid.
While many of these cysts are benign, professional evaluation is necessary if the swelling is persistent, symptomatic, or exhibits any warning signs. An immediate visit to a dentist or doctor is warranted if the bubble is accompanied by intense pain, rapid growth, or a fever, which may indicate an infection. Difficulty swallowing, breathing, or speaking due to the size of the swelling are also signs that require prompt medical attention.
Diagnosis often begins with a visual and physical examination; imaging like an ultrasound may be used to confirm the nature and extent of the fluid collection. For persistent or recurrent ranulas, simple drainage is rarely a permanent solution because the blocked duct leads to a high recurrence rate. Definitive treatment often involves a surgical procedure to remove the cyst and the associated sublingual gland. A less invasive technique called marsupialization involves cutting a slit into the top of the cyst and stitching the edges open to create a new permanent drainage pathway.