Most mouth ulcers are aphthous ulcers, commonly called canker sores, and they form when the delicate lining of your mouth breaks down in response to one or more triggers. These triggers range from something as mundane as biting your cheek to nutritional shortfalls, stress, or an ingredient in your toothpaste. The vast majority heal on their own within a week or two and are not dangerous, but ulcers that keep coming back or refuse to heal sometimes point to an underlying condition worth investigating.
Mechanical Injury Is the Most Obvious Cause
The simplest explanation for a mouth ulcer is physical damage. Biting your tongue or the inside of your cheek, scraping your gums with a hard piece of food, or burning the roof of your mouth with hot coffee can all create a raw spot that develops into a visible ulcer. These traumatic ulcers usually appear exactly where the injury happened and heal once the irritation stops.
Dental hardware is a frequent repeat offender. Braces, dentures, retainers, and even a chipped or sharp-edged tooth can rub the same spot of tissue over and over, preventing it from healing and sometimes turning a minor wound into a chronic ulcer. Chronic traumatic ulcers of the oral cavity are commonly brought on by repeated mechanical stress from friction against dental appliances or sharp and broken teeth.1PubMed Central. Chronic Traumatic Ulcer: A Case Report If you notice a sore that sits right where your denture presses or where a broken filling catches your cheek, that mechanical irritation is the likely culprit. Getting the dental issue fixed often resolves the ulcer entirely.
Your Toothpaste Could Be Contributing
This one surprises a lot of people. Sodium lauryl sulfate, commonly listed as SLS, is a foaming agent found in most mainstream toothpastes. It is also a detergent that strips away the thin mucus layer protecting the inside of your mouth. With that barrier weakened, the underlying tissue is more vulnerable to ulcer formation.
A systematic review of trials comparing SLS-containing and SLS-free toothpastes found that switching to an SLS-free formula reduced the number of ulcers, the duration of each episode, and the pain associated with them.2PubMed. Effect of sodium lauryl sulfate on recurrent aphthous stomatitis: A systematic review An earlier study put numbers on the difference: participants went from an average of about 14 ulcers during a period of using SLS toothpaste down to roughly 5 after switching to an SLS-free version.3PubMed. Sodium lauryl sulfate and recurrent aphthous ulcers. A preliminary study If you get mouth ulcers regularly and have never checked your toothpaste’s ingredient list, this is one of the easiest things to change. SLS-free toothpastes are widely available and work just as well for cleaning your teeth.
Stress and the Hormonal Cascade
Anyone who gets canker sores during exam season or after a terrible week at work already suspects stress plays a role. The research backs this up, though the picture is not perfectly clean. A survey of dental students found that among those with a history of oral ulcers, about 27% linked their outbreaks directly to stressful periods.4PubMed Central. Recurrent Oral Ulcers and Its Association With Stress Among Dental Students in the Northeast Indian Population: A Cross-Sectional Questionnaire-Based Survey That may not sound like a majority, but stress is rarely the only factor at play. It tends to pile on top of other vulnerabilities.
The biological link appears to run through cortisol, your body’s primary stress hormone. One study found that people with recurrent aphthous ulcers had salivary cortisol levels roughly three and a half times higher than those without ulcers, and their anxiety scores were also significantly elevated.5PubMed Central. Relationship of salivary cortisol and anxiety in recurrent aphthous stomatitis Not every study finds such a dramatic difference. Another measured cortisol in ulcer patients and controls and found only a slight, non-significant increase in the ulcer group, with no meaningful difference in anxiety or depression scores between the groups.6PubMed Central. Evaluation the relationship between psychological profile and salivary cortisol in patients with recurrent aphthous stomatitis The disagreement probably reflects how many other variables feed into ulcer risk. Stress alone may not be enough to cause outbreaks in everyone, but for people already predisposed, it can tip the balance.
Nutritional Deficiencies Your Mouth Reveals First
Your mouth’s lining turns over rapidly, replacing itself every one to two weeks. That fast cell turnover demands a steady supply of certain nutrients, and when they run low, the lining can thin out and break down more easily. The most consistently implicated deficiencies involve vitamin B12, folate, and iron.
Research has shown that people with recurrent aphthous ulcers tend to consume lower amounts of vitamin B12 and folate than the general population, not just show lower blood levels of these nutrients.7PubMed Central. Reduced dietary intake of vitamin B12 and folate in patients with recurrent aphthous stomatitis This suggests that the problem is sometimes dietary rather than a hidden absorption issue, which means it can be addressed with food choices or supplements. If you eat very little meat, dairy, or leafy greens, or you follow a restrictive diet, and you get frequent mouth ulcers, it is worth having your B12 and folate levels checked. Iron deficiency, often seen alongside these other shortfalls, contributes in a similar way by impairing the tissue’s ability to repair itself quickly.
Infections That Look Like Canker Sores
Not every mouth ulcer is a canker sore. Viral infections can produce ulcers that look similar but behave differently and sometimes need different management.
The most common viral mimic is recurrent intraoral herpes, caused by herpes simplex virus. The two conditions are frequently confused in clinical settings because both produce painful sores inside the mouth. The key differences come down to location and pattern. Herpes ulcers tend to cluster on the hard palate and attached gingiva (the firm gum tissue around your teeth), whereas canker sores favor the softer, more mobile tissue like the inside of your cheeks, lips, and the floor of your mouth. Herpes outbreaks also typically start with a cluster of tiny blisters that merge and then ulcerate, while canker sores usually appear as a single round or oval sore from the start.
In children, hand, foot, and mouth disease is another common cause of oral ulcers. This infection, driven by enteroviruses, causes painful sores in the mouth along with a rash on the hands and feet. Outbreaks can involve several viral strains, with coxsackievirus A10 and A6 among the most frequently identified.8PubMed. Outbreak of hand, foot and mouth disease/herpangina associated with coxsackievirus A6 and A10 infections in 2010, France These infections are self-limiting, and the oral ulcers clear as the immune system handles the virus, but they can be quite painful while they last.
When Mouth Ulcers Point to a Systemic Disease
Occasional mouth ulcers are usually nothing to worry about. Recurrent or unusually severe ulcers, especially when combined with other symptoms, can be an early sign of a condition that goes well beyond the mouth.
Celiac Disease
Celiac disease damages the small intestine in response to gluten, and one of its lesser-known effects is recurring mouth ulcers. Research has found a strong enough association between the two that recurrent aphthous-like ulcers should be considered a risk indicator for celiac disease, and that following a gluten-free diet leads to improvement in the ulcers.9PubMed. Coeliac disease: oral ulcer prevalence, assessment of risk and association with gluten-free diet in children If you get frequent mouth ulcers and also experience bloating, diarrhea, unexplained fatigue, or weight loss, celiac screening is reasonable.
Inflammatory Bowel Disease
Both Crohn’s disease and ulcerative colitis can produce oral ulcers as an “extraintestinal manifestation,” meaning the disease shows up outside the gut. Aphthous stomatitis and angular cheilitis (cracking at the corners of the mouth) occur in both conditions.10PubMed Central. Oral pathology in inflammatory bowel disease A systematic review specifically focused on Crohn’s disease found that oral ulcers, gingivitis, and angular cheilitis were the most frequent oral manifestations, and their early identification can help achieve an earlier diagnosis.11PubMed Central. Oral Manifestations of Crohn’s Disease: A Systematic Review Sometimes the mouth ulcers appear before any gut symptoms do, which is why dentists and doctors pay attention to patterns of recurrent oral ulceration.
Behçet’s Disease
Behçet’s disease is a rarer condition involving inflammation of blood vessels throughout the body. Oral ulcers are often the earliest and most consistent symptom. A case report described a patient whose recurrent oral ulcers, along with genital ulcers and folliculitis, eventually led to diagnosis after he was hospitalized for deep vein thrombosis.12PubMed Central. Oral Lesions as the Primary Manifestations of Behçet’s Disease: The Importance of Interdisciplinary Diagnostics-A Case Report The ulcers in Behçet’s tend to be large, painful, and recurrent, and they often appear alongside ulcers in other mucous membranes. If you have mouth ulcers recurring alongside sores in other areas of the body, joint pain, or eye inflammation, bring it up with your doctor.
Medications That Cause Mouth Ulcers
Several prescription drugs can trigger oral ulcers as a side effect. The list includes certain chemotherapy agents, immunosuppressants, and some less obvious culprits. One of the better-documented examples is nicorandil, a drug used to treat angina in some countries. Nicorandil has been shown to cause persistent, painful mouth ulcers that can be severe and resist healing for as long as the drug is continued.13PubMed. Nicorandil can induce severe oral ulceration A ten-year analysis of cases reported to France’s pharmacovigilance network found that nicorandil-induced ulcers were mainly mucosal, affecting the mouth and anus, and that a previous trauma to the site was present in about 23% of patients.14PubMed Central. Nicorandil-induced ulcerations: a 10-year observational study of all cases spontaneously reported to the French pharmacovigilance network
Methotrexate, commonly used for rheumatoid arthritis and other autoimmune conditions, is another well-known offender. NSAIDs, certain blood pressure medications, and some antibiotics can also provoke oral ulceration. If you started a new medication in the weeks before your ulcers appeared, it is worth flagging the timing with your prescriber. Drug-induced ulcers often resolve once the medication is stopped or switched.
Cancer Treatment and Oral Mucositis
Radiation and chemotherapy attack rapidly dividing cells, and the lining of the mouth is one of the fastest-turnover tissues in the body. The result is oral mucositis: widespread inflammation and ulceration that can range from mild soreness to severe, debilitating breakdown of the mouth’s lining. Nearly all patients receiving radiotherapy or chemotherapy will experience some degree of it.15PubMed Central. Radiation induced oral mucositis The risk is especially high in people being treated for cancers of the mouth, throat, or nasopharynx, and in those receiving combined radiation and chemotherapy or high total radiation doses.
Mucositis ulcers are distinct from ordinary canker sores in their severity and extent. They can cover large areas of the mouth, make eating and drinking extremely painful, and create openings for secondary infections. Managing them is a significant part of supportive care during cancer treatment.16PubMed Central. Management of oral mucositis in patients who have cancer
The Immune System’s Role
Even when the trigger is something external like stress or a nutrient gap, the actual tissue destruction in a canker sore is carried out by your immune system. In people with recurrent aphthous ulcers, the immune response in the mouth’s lining appears to be disproportionate. Research has found that levels of TNF-alpha, a key inflammatory signaling molecule, are roughly 80% higher in the saliva of people with recurrent ulcers compared to those without.17PubMed Central. Salivary levels of TNF-α in patients with recurrent aphthous stomatitis: A cross-sectional study This heightened inflammatory tone helps explain why some people seem to develop ulcers at the slightest provocation while others rarely get them at all.
The oral microbiome may feed into this inflammatory cycle. Research comparing the bacteria in the mouths of ulcer-prone individuals and controls has found differences in microbial composition, with certain bacterial populations more or less prevalent depending on whether ulcers were actively present.18PubMed Central. The oral microbiota of patients with recurrent aphthous stomatitis Whether these shifts cause the ulcers or result from them is still unclear, but the interplay between immune regulation and the mouth’s microbial community is an active area of research.
Genetics and Family Patterns
If your parents got frequent canker sores, you are more likely to as well. The familial clustering of recurrent aphthous ulcers is well documented, and the heritability appears to involve genes that regulate the immune and inflammatory response. Specifically, people who inherit certain variations in genes encoding pro-inflammatory cytokines, the signaling molecules that drive inflammation, may be predisposed to the overactive mucosal immune response that underlies ulcer formation.19PubMed Central. Recurrent aphthous stomatitis: genetic aspects of etiology This does not mean mouth ulcers are inevitable if they run in your family, but it does mean your threshold for developing them in response to other triggers may be lower.
Hormonal Fluctuations
Many women notice that mouth ulcers flare at particular points in their menstrual cycle, typically in the luteal phase just before a period. The connection has been observed for decades, and hormonal shifts in estrogen and progesterone are thought to influence the vulnerability of the oral mucosa. Some women find that their ulcers improve during pregnancy, when hormone levels are sustained at high levels, and return after delivery. Hormonal contraceptives have also been reported to alter ulcer frequency in some women, though the effect varies. This hormonal link remains one of the less thoroughly studied aspects of recurrent mouth ulcers, partly because it is difficult to isolate hormone effects from the many other factors that co-vary with the menstrual cycle.
When You Should See a Doctor
Most mouth ulcers do not need medical attention. But certain patterns should prompt a visit:
- Duration: A single ulcer that has not healed after three weeks needs professional evaluation. Ordinary canker sores resolve well before that.
- Size: Ulcers larger than about a centimeter, or multiple large ulcers appearing simultaneously, warrant a closer look.
- Recurrence: If you are getting new ulcers before the old ones have healed, or you have outbreaks more than a few times a year, there may be an underlying trigger worth identifying.
- Associated symptoms: Ulcers accompanied by unexplained weight loss, persistent fatigue, fever, skin rashes, genital sores, or gut problems suggest a systemic cause.
- Painlessness: Counterintuitively, a mouth ulcer that does not hurt can be more concerning than one that does. Painless ulcers that fail to heal are a red flag for oral cancer and should be examined promptly.
A thorough diagnostic workup for persistent or complicated oral ulcers typically includes a detailed medical history, examination of the lesion, and sometimes a biopsy or blood tests to screen for systemic diseases.20PubMed Central. Difficult and complicated oral ulceration: an expert consensus guideline for diagnosis The goal is to distinguish between the common, self-limiting canker sore and the less common ulcer that signals something requiring treatment beyond waiting it out.
Simple Things That Help
For ordinary canker sores, the healing environment matters more than most people realize. The mouth is warm, wet, and constantly in motion from talking and chewing, all of which makes it harder for ulcers to heal compared to a wound on your skin.21PubMed Central. Revisited and innovative perspectives of oral ulcer: from biological specificity to local treatment You cannot stop eating or talking, but you can reduce additional irritation. Avoiding acidic, spicy, and crunchy foods while a sore is active makes a real difference. Switching to an SLS-free toothpaste, as noted earlier, can reduce the frequency of future outbreaks. Over-the-counter protective pastes and gels that coat the ulcer create a temporary barrier against friction and food contact, and topical anesthetics containing benzocaine or lidocaine help manage the pain.
For people whose ulcers are frequent enough to affect quality of life, prescription options exist. Corticosteroid mouth rinses or gels reduce the inflammatory response locally. In severe or refractory cases, systemic medications may be considered, though these carry their own side effects and are reserved for situations where simpler measures have failed. Addressing any underlying nutritional deficiency, managing stress, and identifying triggers through a careful diary of outbreaks and possible precipitants can gradually reduce the frequency and severity of episodes over time.