Most mouth ulcers form from everyday physical damage, like biting your cheek, scraping your gums with a sharp chip, or irritation from braces or a rough filling. These small, painful sores on the soft tissue inside your mouth are extremely common, affecting anywhere from 5% to 66% of the population depending on the group studied. While the occasional ulcer is almost always harmless and heals on its own in one to two weeks, recurring ulcers can signal nutritional gaps, immune system quirks, or underlying health conditions worth investigating.
Physical Damage Is the Most Common Cause
The lining of your mouth is delicate, and it doesn’t take much to break it. The most frequent triggers are mechanical: biting the inside of your cheek or tongue, jabbing yourself with a sharp piece of food, brushing too aggressively, or wearing poorly fitting dentures or dental appliances. A rough edge on a filling or a broken tooth can also rub against the same spot repeatedly until a sore develops.
These are called traumatic ulcers. They typically appear as a single sore right at the point of injury, and they heal within one to two weeks once the source of irritation is gone. If a sharp tooth or appliance keeps rubbing the same area, though, the ulcer will stick around until you get the problem fixed.
Your Toothpaste Might Be Making It Worse
Sodium lauryl sulfate (SLS), the foaming agent in most toothpastes, can strip away the protective outer layers of your mouth’s lining. For people who are already prone to ulcers, SLS-containing toothpaste has been shown to increase the frequency of outbreaks. One clinical study found four times fewer soft tissue lesions after switching to an SLS-free toothpaste compared to a standard formula. If you get mouth ulcers regularly, switching to an SLS-free brand is one of the simplest changes you can make.
Nutritional Deficiencies and Recurring Ulcers
People who get mouth ulcers over and over again are significantly more likely to be low in certain nutrients, particularly vitamin B12. In one study comparing ulcer patients to healthy controls, half of the ulcer group had vitamin B12 levels below 220 pg/mL, while none of the control group did. The average B12 level among deficient patients was just 124 pg/mL, well into the range where symptoms appear.
Iron and folate deficiencies also play a role, though the connection isn’t always as clear-cut. Low iron stores (measured by ferritin) appeared in about 10% of ulcer patients in that study. The takeaway: if you’re dealing with ulcers that keep coming back, it’s worth asking your doctor to check your B12, iron, and folate levels. Correcting a deficiency can sometimes reduce or stop the cycle entirely.
Stress, Hormones, and Immune Triggers
Recurrent aphthous stomatitis, the medical term for canker sores that keep returning, involves your immune system overreacting against the tissue lining your mouth. The exact chain of events isn’t fully understood, but the immune system essentially attacks healthy mucosal cells, creating the characteristic painful crater. Stress is one of the most commonly reported triggers, and many women notice ulcers flaring in sync with their menstrual cycle, pointing to a hormonal component.
Certain foods seem to provoke outbreaks in susceptible people. Citrus fruits, tomatoes, chocolate, coffee, and nuts are among the most frequently cited culprits, though the specific triggers vary widely from person to person. Keeping a food diary when ulcers flare can help you identify your personal patterns.
Medications That Cause Mouth Sores
Several common medications can damage the lining of your mouth. NSAIDs like aspirin and naproxen can cause chemical burns to the oral tissue, producing white or yellow lesions that peel and ulcerate. Some blood pressure medications, including certain ACE inhibitors and angiotensin receptor blockers, are also associated with oral tissue damage. If you started a new medication shortly before mouth ulcers appeared, that connection is worth mentioning to your prescriber.
When Ulcers Signal a Bigger Problem
Mouth ulcers are occasionally the first visible sign of a systemic disease. Celiac disease, Crohn’s disease, and other inflammatory bowel conditions can all produce recurrent oral ulcers, sometimes before any gut symptoms develop. Behcet’s disease, a condition involving widespread blood vessel inflammation, lists painful mouth sores as its most common sign. These sores start as raised, round bumps that quickly become painful ulcers, typically healing in one to three weeks but returning frequently.
The pattern matters more than any single ulcer. A one-off sore after biting your cheek is nothing to worry about. But ulcers that recur in clusters, appear alongside sores in other areas of your body, or come with other symptoms like joint pain, digestive issues, or persistent fatigue may warrant further investigation for an underlying condition.
Ulcers That Don’t Heal Need Attention
The critical timeline to know is this: any mouth sore that hasn’t healed within two weeks deserves a closer look. The American Dental Association recommends that clinicians pursue a biopsy or referral when an oral abnormality persists beyond 10 to 14 days without a clear diagnosis and treatment plan. This isn’t because most non-healing ulcers are dangerous, but because oral cancer can look like a stubborn ulcer in its early stages. A single, painless sore that lingers, especially on the side or underside of the tongue or on the floor of the mouth, is the pattern that raises the most concern.
How Mouth Ulcers Are Treated
Most ulcers heal on their own without any treatment. The goal with medication is pain relief and possibly faster healing, not prevention. Topical corticosteroid pastes and pellets applied directly to the sore are the standard first-line option. They reduce pain and inflammation but don’t prevent future outbreaks.
For immediate pain relief, your dentist or doctor may suggest a medicated mouth rinse. One common formulation combines a topical numbing agent, an antacid liquid to help it coat the sore, and an antihistamine. Swishing this mixture several times a day can take the edge off enough to eat and drink comfortably. Antiseptic rinses containing chlorhexidine can also reduce the severity and pain of ulcers, though they won’t make them come back less often.
Over-the-counter options like protective pastes and gels create a barrier over the ulcer, shielding it from further irritation while it heals. Avoiding spicy, acidic, and crunchy foods during an active ulcer makes a noticeable difference in day-to-day comfort. Most minor ulcers resolve completely within one to two weeks regardless of treatment.