The most common reason for a sore on your tongue is a canker sore, a small shallow ulcer that forms on the soft tissues inside your mouth. But tongue sores have a surprisingly long list of possible causes, from biting your tongue in your sleep to vitamin deficiencies to infections. Most are harmless and heal on their own within one to two weeks. A sore that doesn’t heal in that window needs professional evaluation.
Canker Sores: The Most Likely Cause
Canker sores (aphthous ulcers) account for the majority of tongue sores. They typically appear on the sides of the tongue, the floor of the mouth, or the inner cheeks. A canker sore starts as a small red spot and quickly develops into a shallow ulcer with a white, yellow, or gray center surrounded by a smooth red border, sometimes called a “red halo.” They range from about half a centimeter to two centimeters across.
The pain from canker sores is often described as out of proportion to the size of the lesion. A tiny sore can make eating, drinking, and talking genuinely miserable. You might get a single sore or up to five at once. They usually heal without treatment in 7 to 14 days.
Nobody knows exactly what triggers them, but common culprits include stress, lack of sleep, acidic or spicy foods, minor mouth injuries (like biting your cheek), hormonal changes, and certain toothpaste ingredients, particularly sodium lauryl sulfate. If you get canker sores repeatedly, it’s worth tracking what happened in the days before each outbreak.
Cold Sores on the Tongue
Cold sores caused by the herpes simplex virus can occasionally appear inside the mouth, though they more commonly show up on the lips, hard palate, or gums. They look different from canker sores. Instead of a single round ulcer, herpes lesions start as a cluster of tiny gray-white blisters, each about a millimeter across, that burst and merge into a larger sore with an irregular, scalloped edge.
The other key difference is how they begin. Before a cold sore appears, you’ll often feel a tingling, burning, or throbbing sensation in the area, sometimes preceded by a strange numbness. That warning phase, called the prodrome, typically lasts 24 to 48 hours before blisters develop. Canker sores don’t have this distinct buildup. They just start as localized discomfort right at the spot where the ulcer forms.
Physical Trauma and Irritation
Sometimes the explanation is mechanical. You bit your tongue while eating, burned it on hot coffee, or scraped it against a sharp edge on a tooth or dental appliance. These injuries create sores that look red, raw, or slightly swollen. They’re usually easy to identify because you remember when the pain started and can often feel the source of irritation with your tongue.
Less obvious is nighttime damage. Grinding or clenching your teeth during sleep can injure the edges of your tongue over time, creating recurring sores in the same spots. Roughly one-third of people with burning mouth syndrome have a tooth-grinding or jaw-clenching habit that contributes to their symptoms. If you wake up with a sore tongue regularly, especially along the sides, this is worth investigating with a dentist.
Nutrient Deficiencies
A sore, red, or inflamed tongue can be a sign that your body is low on certain nutrients. Vitamin B12 deficiency and folate deficiency both cause tongue soreness, sometimes accompanied by mouth ulcers. Iron deficiency does the same. The tongue may look unusually smooth because the tiny bumps on the surface (papillae) flatten out, and it can feel raw or burning.
Other symptoms of these deficiencies include fatigue, pale skin, breathlessness, and feeling weak. If your tongue sores keep coming back and you also feel unusually tired, a simple blood test can check your levels. This is especially common in people who follow restrictive diets, have absorption issues, or are pregnant.
Oral Thrush
Thrush is a fungal infection caused by an overgrowth of yeast that naturally lives in your mouth. It creates white or cream-colored patches on the tongue and inner cheeks that can be wiped off, revealing red, raw tissue underneath. It may feel sore or produce a cottony sensation in your mouth.
Thrush is more common after a course of antibiotics, in people who use inhaled corticosteroids for asthma, in those with weakened immune systems, and in people with diabetes. It’s treatable with antifungal medication.
Geographic Tongue
If the sore patches on your tongue are smooth, irregularly shaped, and seem to move around over days or weeks, you may have geographic tongue. This condition creates areas where the tiny surface bumps disappear, leaving smooth red patches bordered by raised white or yellowish edges. The pattern shifts as patches heal in one area and appear in another, giving the tongue a map-like appearance.
Geographic tongue is harmless and doesn’t need treatment. Some people notice sensitivity to hot or spicy foods on the affected areas, but otherwise it causes no lasting problems. It tends to come and go over months or years.
Lichen Planus
Oral lichen planus is an inflammatory condition that shows up in two main forms. The more common version creates a white, lacy pattern on the tongue or inner cheeks that may not hurt at all. The second form, erosive lichen planus, produces shallow ulcerations that can be persistently sore. These sores tend to stick around longer than canker sores and may need a biopsy to confirm the diagnosis. Lichen planus can also coexist with a fungal infection, which needs separate treatment.
Less Common but Serious Causes
Syphilis can produce sores on the tongue, though this is uncommon. A primary syphilis sore (chancre) is firm, round, painless, and oozes fluid. It typically lasts one to five weeks and heals on its own, which can be misleading because the infection is still progressing. In the secondary stage, flat patches called mucous patches can form on the underside of the tongue. Because these sores are painless, they’re easy to dismiss.
Oral cancer is the cause most people worry about, and while it’s far less common than canker sores, it’s important to know the warning signs. A malignant lesion on the tongue is typically persistent, meaning it doesn’t heal within two weeks. It may be red, a mix of red and white, or ulcerated. It often feels firm or hardened when you press on it, and it may be fixed to the tissue beneath rather than movable. Rapid growth or easy bleeding are additional red flags.
How to Care for a Tongue Sore at Home
For garden-variety canker sores and minor injuries, a saltwater or baking soda rinse is the simplest and most effective home remedy. Memorial Sloan Kettering Cancer Center recommends mixing one teaspoon of salt and one teaspoon of baking soda into one quart (four cups) of water. Rinse every four to six hours. You can also use salt alone or baking soda alone in the same ratio. The rinse helps keep the area clean and creates an environment that supports healing.
Avoid foods that aggravate the sore: anything acidic (citrus, tomatoes), very spicy, salty, or rough-textured. Soft, cool foods are easier to tolerate. Over-the-counter numbing gels containing benzocaine can temporarily reduce pain, though they wear off quickly.
For more stubborn or painful canker sores, a prescription steroid dental paste can reduce inflammation and speed healing. It’s applied as a thin film directly over the sore, ideally at bedtime so it stays in contact with the tissue overnight. If the sore hasn’t improved within seven days of using it, further investigation is recommended.
When a Tongue Sore Needs Attention
The general rule is two weeks. Most benign tongue sores, whether from trauma, canker sores, or minor infections, resolve within that window. A sore that persists beyond two weeks after any obvious irritant is removed warrants a professional evaluation, and a biopsy is strongly recommended for any lesion that sticks around that long.
Seek evaluation sooner if the sore is painless but firm, bleeds easily, grows rapidly, or is accompanied by a lump in your neck. Also worth getting checked: sores that keep recurring in the exact same spot, sores that appear alongside unexplained fatigue or weight loss, and any sore paired with a new skin rash, which could suggest a systemic condition like syphilis or lichen planus affecting multiple areas of the body.