Tongue ulcers are most commonly caused by canker sores, which affect 10 to 20 percent of the general population and result from a combination of immune system dysfunction, physical injury, and genetic predisposition. Less often, tongue ulcers signal an infection, a nutritional deficiency, or a systemic disease. Most heal on their own within two weeks, but an ulcer that lingers beyond that point deserves a closer look.
Canker Sores: The Most Common Cause
The vast majority of tongue ulcers are canker sores, known medically as recurrent aphthous stomatitis. These are shallow, round or oval sores with a white or yellowish center and a red border. They form inside the mouth, on the tongue, inner cheeks, or gums, and they tend to come back over time.
The exact cause isn’t fully understood, but it likely involves several overlapping factors: an overactive or misdirected immune response, a genetic tendency (they run in families), and environmental triggers. Stress, poor sleep, hormonal shifts during menstruation, and certain foods like citrus fruits, tomatoes, and spicy dishes are well-known triggers in people who are prone to them.
Minor canker sores, the most common type, typically heal in 10 to 14 days without treatment. Major canker sores are larger, deeper, and can last up to a month. A third type, called herpetiform ulcers, appears as clusters of tiny sores that can merge into larger, irregularly shaped ulcers. These are especially painful and can persist anywhere from 10 to 100 days, making eating and speaking extremely difficult.
Physical Injury to the Tongue
Biting your tongue during chewing or in your sleep is one of the simplest and most overlooked causes of tongue ulcers. Sharp or broken teeth, rough dental fillings, and orthodontic braces can repeatedly scrape the same spot on the tongue, creating a sore that struggles to heal because the irritation never stops. Ill-fitting dentures cause the same problem.
These traumatic ulcers usually appear right at the point of contact and have an irregular shape that mirrors the source of injury. The fix is often straightforward: smoothing down a jagged tooth, repairing a broken filling, or adjusting braces or dentures removes the cause and lets the tissue heal.
Toothpaste Ingredients
A surprisingly common trigger hides in your bathroom. Sodium lauryl sulfate (SLS), the foaming agent in most toothpastes, irritates the soft tissue inside the mouth and can provoke canker sores in susceptible people. In one study, participants who switched to an SLS-free toothpaste experienced roughly a 70 percent reduction in ulcer episodes compared to their baseline. Even compared to using a toothpaste containing SLS, the reduction was about 60 percent. If you get frequent tongue ulcers, switching to an SLS-free toothpaste is a simple, low-cost change worth trying.
Nutritional Deficiencies
Your tongue is one of the first places a nutritional gap shows up. Low levels of iron, vitamin B12, folate, or zinc are all linked to recurrent mouth ulcers. These deficiencies compromise the body’s ability to maintain and repair the delicate lining of the mouth. The ulcers often look identical to ordinary canker sores, which is why the connection can go unnoticed for months or years. A blood test can identify the shortfall, and correcting it with diet or supplements typically reduces how often the sores return.
Viral and Bacterial Infections
Herpes simplex virus type 1 (HSV-1) causes cold sores, which are fluid-filled blisters that typically appear on or around the lips. The virus lives dormant in nerve cells and periodically reactivates, traveling to the skin surface. While cold sores usually form outside the mouth, the initial HSV-1 infection (most common in childhood) can cause widespread sores inside the mouth, including on the tongue. These look like clusters of small blisters that break open into shallow ulcers.
The key distinction: canker sores form inside the mouth and are not contagious. Cold sores form outside the mouth, are highly contagious, and are caused by a virus. However, during a first-time herpes infection, the lines blur, and sores can appear almost anywhere in the oral cavity.
Other infections that can cause tongue ulcers include hand, foot, and mouth disease (common in young children), oral thrush (a fungal overgrowth that can leave raw patches), and syphilis, which sometimes produces a painless ulcer on the tongue as an early sign.
Systemic Diseases
Tongue ulcers that keep returning despite no obvious trigger can sometimes point to a broader condition affecting the whole body. Behçet’s disease, a rare inflammatory disorder, causes mouth sores in virtually all patients. These sores look like ordinary canker sores but are more numerous, more frequent, and more painful. They appear on the lips, tongue, and inner cheeks, and are often the very first symptom a person notices, sometimes appearing years before other signs of the disease develop.
Inflammatory bowel diseases like Crohn’s disease can also produce oral ulcers. Celiac disease is another culprit, because the immune reaction to gluten can damage the mouth lining and create nutritional deficiencies that compound the problem. Conditions that suppress the immune system, including HIV and the side effects of chemotherapy, make the mouth more vulnerable to ulceration as well.
When a Tongue Ulcer Could Be Cancer
Most tongue ulcers are harmless, but oral cancer can start as a sore on the tongue that simply doesn’t heal. The two-week rule is the standard guideline: any mouth sore that persists beyond two weeks without improvement should be evaluated. Unlike a canker sore, a cancerous ulcer is often painless in its early stages, may feel firm or raised at the edges, and does not follow the typical pattern of healing on its own.
Other warning signs of oral cancer include a white or reddish patch inside the mouth, a lump or thickening of tissue, difficulty or pain when swallowing, unexplained ear pain, and loose teeth with no dental explanation. Tobacco use, heavy alcohol consumption, and HPV infection all raise the risk. Squamous cell carcinoma accounts for the large majority of oral cancers, and the tongue is one of the most common sites.
Reducing Tongue Ulcer Frequency
For people who deal with recurrent canker sores, several practical steps can reduce flare-ups. Switching to an SLS-free toothpaste is one of the most effective changes. Avoiding known food triggers, managing stress, and getting adequate sleep all help. If you suspect a nutritional gap, testing your iron, B12, folate, and zinc levels gives you a clear target to correct.
Keeping the mouth clean with gentle brushing and a mild, alcohol-free mouthwash supports healing when an ulcer does appear. Over-the-counter topical gels that form a protective barrier over the sore can ease pain during eating. For severe or frequent outbreaks, prescription options exist that target the underlying immune response.