Tongue sores most often come from canker sores, minor injuries, or irritation, and they typically heal on their own within one to two weeks. But a surprisingly wide range of factors can trigger them, from vitamin deficiencies and toothpaste ingredients to immune conditions and infections. Understanding the cause behind your tongue sore helps you figure out whether it needs attention or just time.
Canker Sores: The Most Common Culprit
Canker sores (aphthous ulcers) are the single most frequent cause of tongue sores. They appear as round white or yellow spots with a red border, usually on the tongue, inner cheeks, or inside the lips. They’re not contagious and not caused by a virus. In fact, they don’t have a definitively known cause, though several triggers are well established: stress, mouth injuries, smoking, and deficiencies in folic acid, iron, or vitamin B12.
Food allergies can also play a role. If you get canker sores regularly, an allergic reaction to certain foods may be triggering outbreaks. Most canker sores heal within a week or two without treatment, but they can be painful enough to make eating and talking uncomfortable in the meantime.
Canker sores are sometimes confused with cold sores, but the two are very different. Cold sores are caused by herpes simplex virus (usually type 1), appear as fluid-filled blisters, and almost always show up outside the mouth around the lips. They’re highly contagious. Canker sores stay inside the mouth and can’t be passed to someone else.
Physical Injury and Irritation
Biting your tongue during chewing is an obvious cause, but it’s not the only mechanical trigger. Sharp or broken fillings, chipped teeth, and rough edges on dental work can repeatedly scrape the tongue and create sores that don’t heal well because the irritation never stops. Orthodontic brackets and poorly fitting dentures cause similar problems. If a tongue sore keeps coming back in the same spot, a sharp dental surface is a likely explanation, and smoothing or repairing the offending tooth or filling often resolves it.
Burns from hot food or drinks are another frequent cause. These usually heal quickly but can feel disproportionately painful because the tongue has such a dense concentration of nerve endings.
Your Toothpaste May Be Making It Worse
Sodium lauryl sulfate (SLS), a foaming agent in most commercial toothpastes, can damage the protective lining of the mouth. It works by stripping away the mucin layer that normally shields your oral tissue, leaving the tongue and cheeks more vulnerable to irritation and sores. At concentrations found in many toothpastes, SLS breaks down the outer layer of cells in the mouth rather than just cleaning them.
Research on people who get recurring canker sores found that switching to an SLS-free toothpaste reduced both the healing time and pain levels of ulcers. A meta-analysis of four clinical trials concluded that people prone to canker sores who used SLS-free toothpaste experienced fewer ulcers, shorter episodes, and less pain overall. If you deal with frequent tongue sores, this is one of the simplest changes to try.
Vitamin Deficiencies
Low levels of vitamin B12, iron, and folate are strongly linked to recurring tongue sores. B12 deficiency in particular can cause a distinctive condition called glossitis, where the tongue becomes swollen, smooth, and “beefy” red, losing its normal texture. People with B12 deficiency also report burning sensations on the tongue, lips, and inner cheeks, along with changes in taste.
These deficiencies don’t just cause sores directly. They impair the body’s ability to maintain healthy tissue in the mouth, making the tongue more susceptible to ulcers from even minor irritation. B12 deficiency is especially common in older adults, vegetarians, and people with absorption problems like pernicious anemia. If your tongue sores keep coming back without an obvious trigger, a blood test checking B12, iron, and folate levels is a reasonable step.
Oral Thrush
Oral thrush is a fungal infection caused by an overgrowth of Candida, a yeast that normally lives in the mouth in small amounts. When the balance tips, it produces creamy white patches on the tongue and inner cheeks that look like cottage cheese. These patches can bleed slightly when scraped and often come with a burning sensation, a cottony feeling in the mouth, and loss of taste.
Several things make thrush more likely: antibiotics (which kill bacteria that normally keep Candida in check), inhaled corticosteroids for asthma, uncontrolled diabetes, dry mouth, dentures, and any condition that weakens the immune system. Babies and older adults are more susceptible because of naturally lower immune function.
Autoimmune and Digestive Conditions
Tongue sores sometimes signal a problem elsewhere in the body. Celiac disease is a prime example. In studies comparing people with celiac disease to the general population, about 34% of those with celiac disease had recurring canker sores, compared to roughly 13% of people without it. The connection appears to involve the immune response triggered by gluten: elevated inflammatory markers and a shift toward pro-inflammatory signaling that disrupts the mouth’s mucosal lining.
Inflammatory bowel disease and Behçet’s disease share a similar pattern. Researchers have proposed that all three conditions, along with recurring canker sores, involve a common underlying problem: dysregulated mucosal immunity. In some cases, recurring mouth ulcers are the first noticeable symptom of celiac disease, appearing before any digestive complaints.
Oral lichen planus is another immune-mediated condition that affects the tongue. It primarily shows up on the inner cheeks, gums, and the top surface of the tongue as white, lacy patches in its mild form. More troublesome variants cause red, eroded areas that hurt and bleed. The condition results from the immune system’s own cells attacking the base layer of the mouth’s lining. Diagnosis requires both a visual exam and a biopsy, and the condition tends to be chronic.
When a Tongue Sore Could Be Serious
Most tongue sores are harmless, but some features raise concern. Two types of precancerous patches deserve attention: white patches that can’t be scraped off (leukoplakia) and red, velvety patches (erythroplakia). Erythroplakia carries a particularly high risk because it almost always contains abnormal cell changes. Tongue cancer can also present as a firm, thickened area that feels different from the surrounding tissue when you press on it.
The key timeline to remember is two weeks. Any oral lesion that persists or worsens after two weeks warrants a professional evaluation and, in many cases, a biopsy. Benign canker sores resolve within that window. A sore that doesn’t is behaving differently and needs a closer look, especially if it’s painless, firm to the touch, or accompanied by a lump in the neck.