Tongue sores are almost always canker sores, and they’re not dangerous. These small, painful ulcers affect roughly 20% of people at some point and typically heal on their own within one to two weeks. But not every sore on your tongue is a canker sore, and a few other causes are worth knowing about, especially if the sore looks unusual, keeps coming back, or won’t go away.
Canker Sores: The Most Likely Cause
Canker sores (aphthous ulcers) are the most common reason for a painful spot on your tongue. They appear as white or yellowish oval sores with a red border, and they form only on soft, movable tissue: the tongue, the inside of your cheeks, and the inner lips. They’re not contagious and have nothing to do with the herpes virus.
Most canker sores are the minor type, less than 1 cm across, and they heal without scarring in 7 to 14 days. Major canker sores are larger, can appear anywhere in the mouth including the back of the throat, and may take up to six weeks to resolve. These often leave scars. A third, less common variety called herpetiform canker sores can erupt in clusters of up to 100 tiny ulcers at once, each only a few millimeters wide.
The exact cause isn’t fully understood, but common triggers include biting your tongue, stress, hormonal shifts, acidic or spicy foods, and an ingredient in many toothpastes called sodium lauryl sulfate (SLS). SLS is the foaming agent in most commercial toothpastes, and clinical trials have found that people who switch to an SLS-free toothpaste experience fewer canker sores that heal faster and hurt less. If you get canker sores regularly, switching toothpaste is one of the simplest things you can try.
Canker Sores vs. Cold Sores
People often confuse these two, but the distinction is straightforward. Canker sores form inside the mouth. Cold sores (fever blisters) form outside the mouth, typically around the border of the lips. Cold sores are caused by the herpes simplex virus, start as fluid-filled blisters, and are contagious. Canker sores are neither viral nor contagious. If your sore is on your tongue or inner cheek, it’s almost certainly a canker sore, not a cold sore.
That said, a primary herpes infection (the first time you catch the virus) can cause numerous small blisters throughout the mouth, including on the tongue. This usually happens in childhood, comes with fever and swollen gums, and is distinct from the occasional single sore that pops up later in life.
Oral Thrush
If the sore on your tongue looks more like a white patch than a round ulcer, oral thrush may be the cause. Thrush is a yeast infection that produces creamy white spots, sometimes described as looking like cottage cheese, on the tongue, inner cheeks, and roof of the mouth. The key feature: these white patches can be wiped or scraped off, revealing red, slightly bleeding tissue underneath.
Thrush is more common in people who wear dentures, use inhaled corticosteroids for asthma, have a weakened immune system, or have recently taken antibiotics. It’s treatable with antifungal medication. A related condition called median rhomboid glossitis appears as a smooth, red, diamond-shaped patch on the top of the tongue where the tiny bumps (papillae) have flattened out. This is also caused by yeast overgrowth and is generally harmless.
Geographic Tongue
Geographic tongue creates smooth, red patches on the tongue surface surrounded by raised white or light-colored borders, giving the tongue a map-like appearance. The patches shift position over days or weeks, which is why it’s also called benign migratory glossitis. It can cause mild burning or sensitivity to certain foods, but it’s completely harmless and doesn’t require treatment.
Geographic tongue can look alarming the first time you notice it. A doctor or dentist can usually diagnose it on sight. It sometimes needs to be distinguished from oral lichen planus, a different condition that produces lacy white patterns on the inner cheeks and tongue and can cause painful sores. Lichen planus tends to stay in one place rather than migrating, and the white pattern looks more like fine, branching lines than smooth borders.
Vitamin Deficiencies
A sore, red, or swollen tongue, sometimes accompanied by mouth ulcers, can be a sign of vitamin B12 or folate deficiency. Iron deficiency can cause similar symptoms. These deficiencies lead to a condition called glossitis, where the tongue becomes inflamed, changes color, and loses its normal texture. You might also notice fatigue, weakness, or pale skin.
This is worth considering if your tongue soreness is persistent and generalized rather than a single ulcer, especially if you follow a restricted diet, are pregnant, or have a condition that affects nutrient absorption. A simple blood test can confirm or rule out deficiency.
Irritants and Mechanical Causes
Sometimes the explanation is purely physical. A sharp edge on a broken tooth, a rough dental filling, or ill-fitting braces can repeatedly irritate the same spot on your tongue until it becomes an open sore. Burning your tongue on hot food or drinks damages the surface tissue and can leave a painful spot for several days. Acidic foods like citrus, tomatoes, and pineapple can irritate existing sores or trigger new ones in people who are prone to canker sores.
Habitual tongue biting or cheek chewing, often done unconsciously during stress or sleep, is another frequent culprit. If your sores consistently appear in the same location, look for a mechanical cause like a rough tooth edge pressing against that exact spot.
When a Tongue Sore Needs Attention
Most tongue sores heal within two weeks. The timeline matters because sores that persist beyond two to three weeks without improving are considered potentially concerning by medical guidelines. The Oral Cancer Foundation recommends that any oral lesion lasting longer than two to four weeks be evaluated by a specialist to get a definitive diagnosis.
Oral cancer can appear as a sore that won’t heal, a red or white patch, or a lump on the tongue. Leukoplakia, a white plaque that cannot be wiped away, and erythroplakia, a smooth red patch, are precancerous changes that also need evaluation. These are typically painless, which is part of what makes them easy to overlook. Tobacco use, heavy alcohol consumption, and HPV infection are the major risk factors.
Pay attention to any tongue sore that doesn’t heal within three weeks, grows in size, bleeds without obvious cause, or is accompanied by a lump in the neck. A single canker sore that resolves in its usual timeframe is not a reason for concern, even if it’s quite painful while it lasts.
Relieving the Pain at Home
For ordinary canker sores, over-the-counter topical gels containing 20% benzocaine can numb the area and provide temporary relief. Apply a small amount directly to the sore before meals to make eating less painful. Rinsing with warm salt water (half a teaspoon of salt in a cup of water) several times a day helps keep the area clean and can speed healing slightly.
Avoid foods that make the pain worse: anything sharp or crunchy, highly acidic, or very spicy. Soft, cool foods are easiest to tolerate. If you’re getting canker sores more than a few times a year, try switching to an SLS-free toothpaste for a couple of months to see if the frequency drops. Look at the ingredients list on your current tube for “sodium lauryl sulfate,” as it’s present in most mainstream brands.
For sores caused by thrush, over-the-counter remedies won’t resolve the underlying yeast infection. You’ll need an antifungal prescribed by a doctor or dentist. For geographic tongue, no treatment is necessary, though avoiding hot or spicy foods during flare-ups can reduce discomfort.