A sore under your tongue is most often a canker sore, a small shallow ulcer that forms on the soft tissue of the mouth. These are the single most common cause of mouth sores, and the area under the tongue and along the floor of the mouth is one of their favorite spots. But other conditions can cause a sore in this location too, from physical injury to salivary gland problems, and knowing what to look for helps you figure out what you’re dealing with.
Canker Sores: The Most Likely Cause
Canker sores (aphthous ulcers) are small, shallow lesions that develop on the soft tissues inside your mouth, including under the tongue, along the base of the gums, and on the inner cheeks. They typically appear as round or oval spots with a white or yellowish center and a red border. Most are small, under a centimeter across, and heal on their own within one to two weeks.
The exact cause of canker sores isn’t fully understood, but researchers believe a combination of triggers brings them on. Common ones include minor mouth injuries (biting your cheek, aggressive tooth brushing, dental work), stress, hormonal shifts, and certain acidic or spicy foods. Your immune system also plays a role. In some people, the body’s defenses mistakenly attack healthy cells in the mouth lining, creating the ulcer.
Canker sores are not caused by the herpes virus and are not contagious. That’s an important distinction from cold sores, which are viral and typically appear on or around the lips rather than under the tongue.
Physical Injury to the Floor of the Mouth
The tissue under your tongue is thin and delicate, which makes it vulnerable to trauma. A sharp chip on a tooth, rough edge on a dental filling, or orthodontic hardware like braces and wires can rub against this area repeatedly. That constant friction breaks down the tissue and creates an ulcer that looks a lot like a canker sore but has a clear mechanical cause.
You can also injure this area by eating crunchy, sharp-edged foods (think tortilla chips or crusty bread), burning it with hot food or drinks, or accidentally biting down on the underside of your tongue. These traumatic sores usually heal within a week or two once the irritation stops. If you suspect a sharp tooth edge or dental appliance is the culprit, getting it smoothed or adjusted speeds up healing significantly.
Nutritional Deficiencies
If you get sores under your tongue repeatedly, your diet may be part of the problem. Research has found that people with recurrent mouth ulcers have significantly lower daily intakes of vitamin B12 and folate compared to people who don’t get them. Iron deficiency is another common finding. In screening studies, roughly 14 to 18 percent of people with recurrent canker sores turned out to have a nutritional deficiency driving the problem.
What’s notable is that mouth sores and tongue inflammation can sometimes be the only visible sign of an early B12 or folate deficiency, appearing before other symptoms like fatigue or nerve tingling show up. When people with these deficiencies receive vitamin replacement, their mouth sores typically improve. If your sores keep coming back and you can’t identify an obvious trigger, a simple blood test for B12, folate, and iron levels is worth pursuing.
Ranulas and Mucoceles
Not every bump under the tongue is an ulcer. A ranula is a fluid-filled cyst that forms in the floor of the mouth when a salivary gland duct gets blocked or damaged. It looks distinctly different from a canker sore: a ranula appears as a large, soft, translucent or bluish swelling, often described as resembling the belly of a frog. It doesn’t blanch (turn white) when you press on it.
Ranulas develop when saliva leaks from a damaged duct and pools in the surrounding tissue. Trauma is the most common cause, though salivary stones and chronic inflammation can also block the duct. They’re painless or mildly uncomfortable rather than sharply painful, and they tend to grow slowly. Small ones sometimes resolve on their own, but larger or recurring ranulas often need to be treated by a dentist or oral surgeon.
Salivary Stones
Salivary glands sit under and behind your tongue, and the ducts that drain them open into the floor of your mouth. When minerals in your saliva crystallize, they can form small stones that partially or fully block these ducts. The hallmark symptom is swelling and pain under the tongue that gets worse during meals, when the gland ramps up saliva production but the fluid has nowhere to go.
The pain is usually on one side only, and you may notice the swelling comes and goes in a cyclical pattern tied to eating. If a stone is large enough, you or your dentist may be able to see or feel it as a hard lump near the duct opening under your tongue. Smaller stones sometimes pass on their own with hydration and gentle massage. Larger ones may need to be removed.
When a Sore Needs Professional Evaluation
Most sores under the tongue are harmless and heal within one to two weeks. The timeline matters. The American Dental Association recommends that any oral abnormality persisting beyond 10 to 14 days without a clear diagnosis should be biopsied or referred to a specialist. The Mayo Clinic uses a similar two-week benchmark for mouth cancer screening.
Oral cancer can develop on the floor of the mouth and may initially look like a simple sore. Warning signs that set it apart from a canker sore include a lesion that doesn’t heal, a white or reddish patch, a lump or thickened area, pain that radiates to the ear, difficulty swallowing, or loose teeth. The floor of the mouth is actually one of the higher-risk sites for oral cancer, which is why a non-healing sore in this location deserves attention.
Relieving Pain While It Heals
For a typical canker sore or minor traumatic ulcer, over-the-counter numbing gels containing benzocaine (brands like Orajel and Anbesol) provide temporary pain relief by dulling the nerve endings at the sore’s surface. You apply the gel directly to the dried ulcer as needed. Prescription options include a steroid paste that reduces inflammation and speeds healing when applied two to four times daily.
Beyond medication, a few practical steps help. Avoid acidic foods (citrus, tomatoes), spicy dishes, and rough or crunchy textures that scrape the area. Rinsing with warm salt water several times a day can soothe irritation. Switch to a soft-bristled toothbrush and brush gently around the sore. If a sharp tooth or dental appliance is causing repeated injury, getting it addressed prevents the next sore from forming.