Most tongue sores are canker sores, small shallow ulcers triggered by minor injuries, stress, or certain foods. They heal on their own within one to two weeks and are not contagious. But tongue sores can also result from infections, nutritional deficiencies, autoimmune conditions, and, less commonly, precancerous changes. Understanding the pattern, appearance, and timing of your sores helps narrow down what’s behind them.
Canker Sores: The Most Common Cause
Canker sores (aphthous ulcers) are the single most frequent reason people develop painful spots on the tongue. They form inside the mouth, on or under the tongue, along the inner cheeks, or at the base of the gums. They look like small, round or oval ulcers with a white or yellowish center and a red border. The exact cause isn’t fully understood, but a combination of triggers is usually involved.
Known triggers include:
- Mouth injuries: biting your tongue, overly aggressive brushing, dental work, or sports impacts
- Food sensitivities: chocolate, coffee, strawberries, eggs, nuts, cheese, and spicy or acidic foods
- Toothpaste ingredients: products containing sodium lauryl sulfate, a foaming agent
- Hormonal shifts: particularly around menstruation
- Emotional stress
- Nutritional gaps: low levels of vitamin B12, iron, zinc, or folate
Some people get canker sores because of an immune system that mistakenly attacks healthy cells in the mouth lining. The stomach bacterium H. pylori, the same organism behind peptic ulcers, has also been linked to recurrent outbreaks. A single canker sore that heals in a week or two is rarely a concern. Frequent recurrences, clusters of large sores, or sores that last longer than three weeks deserve a closer look.
Biting, Braces, and Other Physical Injuries
A surprisingly large number of tongue sores come down to simple mechanical damage. Accidentally biting your tongue during chewing or sleep, scraping it against a chipped tooth, or irritating it with braces, retainers, or ill-fitting dentures can all produce ulcers that look and feel just like canker sores. These traumatic ulcers typically appear right at the site of contact and heal once the source of irritation is removed. If you notice sores that keep returning in the same spot, a sharp tooth edge or dental appliance rubbing against the tongue is a likely culprit. Switching to a soft-bristled toothbrush can also reduce tissue irritation.
Nutritional Deficiencies
Your tongue is one of the first places a vitamin or mineral shortage shows up. Deficiencies in vitamin B12, folate, and iron are responsible for recurrent mouth ulcers in roughly 18% to 28% of people who are low in these nutrients. B12 deficiency in particular can cause a condition where the tongue becomes smooth, red, and swollen, with fissuring and a gradual loss of the small bumps (papillae) that cover the surface. This affects up to 25% of people with B12 deficiency and often starts as a burning or soreness before visible changes appear.
Other oral signs of B12 deficiency include a persistent burning sensation, changes in taste, dry mouth, and cracked corners of the lips. Iron deficiency tends to produce a pale, smooth tongue alongside general fatigue. If your tongue sores keep coming back and you can’t pin them on an obvious trigger like stress or injury, a blood test checking B12, folate, and iron levels is a reasonable next step.
Oral Thrush
Oral thrush is a yeast infection caused by an overgrowth of Candida, a fungus that normally lives in your mouth in small amounts. It produces creamy white patches on the tongue and inner cheeks that look like cottage cheese and are slightly raised. Scraping or rubbing these patches can cause light bleeding. Other signs include a cottony feeling in the mouth, redness or burning, loss of taste, and difficulty swallowing.
Thrush is more common in babies, older adults, and people with weakened immune systems. Uncontrolled diabetes raises your risk because higher sugar levels in saliva feed the fungus. Antibiotics can trigger it by disrupting the normal balance of organisms in your mouth, and inhaled corticosteroids (often used for asthma) are another frequent cause. Unlike canker sores, thrush won’t resolve on its own and typically requires antifungal treatment.
Cold Sores and Herpes Simplex
Cold sores are caused by the herpes simplex virus (HSV-1) and usually appear as clusters of small, fluid-filled blisters around the outside of the lips. They occasionally develop inside the mouth during a first-time infection, particularly on the hard palate and gums, and can affect the tongue. The key difference between a cold sore and a canker sore is location: cold sores classically form outside the mouth, while canker sores form inside it. Cold sores are also contagious, while canker sores are not. A primary HSV-1 infection in the mouth can cause widespread painful sores, fever, and swollen gums, especially in children.
Geographic Tongue
Geographic tongue creates smooth, red, irregularly shaped patches on the top or sides of the tongue, often with slightly raised borders. The pattern shifts over days or weeks, with patches changing in size, shape, and location, giving the tongue a map-like appearance. The cause is unknown, though it may run in families and has been loosely associated with psoriasis. Geographic tongue is harmless, but the red patches can be sensitive to spicy, acidic, or hot foods. It doesn’t require treatment and isn’t a sign of infection or cancer.
Oral Lichen Planus
Oral lichen planus is a chronic inflammatory condition driven by the immune system. White blood cells involved in inflammation (T lymphocytes) become activated and attack the lining of the mouth for reasons that aren’t well understood. In its erosive form, it produces red, swollen tissues or open sores on the tongue, along with painful, thickened patches. Eating, speaking, and brushing can all become uncomfortable. Hot, acidic, and spicy foods tend to intensify the pain. Oral lichen planus doesn’t go away on its own and cycles between flare-ups and calmer periods, so ongoing management is usually needed.
Underlying Diseases That Cause Mouth Ulcers
Persistent or frequently recurring tongue sores can be a sign of a systemic condition. Celiac disease, an autoimmune reaction to gluten, commonly causes mouth ulcers that may be the earliest or only noticeable symptom. Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis are also associated with recurrent oral sores. HIV/AIDS suppresses the immune system in ways that make the mouth vulnerable to ulcers, thrush, and other infections.
Behçet’s disease is a rarer cause worth knowing about if your mouth ulcers come with other symptoms. It causes inflammation throughout the body, and a diagnosis is typically considered when someone has had at least three episodes of mouth ulcers over 12 months along with at least two of these: genital ulcers, eye inflammation, unusual skin lesions, or hypersensitive skin that reacts strongly to minor injuries.
When a Tongue Sore Could Be Precancerous
Most tongue sores are benign, but certain types of patches warrant attention. Leukoplakia appears as a firm white patch that can’t be scraped off. Erythroplakia is a fiery red, sharply defined patch. Mixed lesions combining red and white areas are also possible. These patches are painless in many cases, which is part of what makes them easy to overlook.
The risk they carry varies significantly by type. Uniform white patches (homogeneous leukoplakia) progress to cancer in about 6% of cases. Non-uniform patches, especially those mixing red and white or appearing speckled, show severe precancerous changes or outright cancer in at least 85% of cases. Lesions on the sides and underside of the tongue carry a higher risk of becoming malignant than similar patches elsewhere in the mouth. Any white or red patch on your tongue that doesn’t heal within two to three weeks, especially if it’s painless and you can’t explain it, is worth having evaluated promptly.