Most mouth ulcers can’t be eliminated entirely, but you can significantly reduce how often they appear by managing a handful of known triggers: mechanical irritation, certain toothpaste ingredients, nutritional gaps, stress, and specific foods. Since the exact cause of recurrent mouth ulcers (also called canker sores) involves immune system dysfunction, genetics, and environmental factors all at once, prevention works best as a combination of small, practical changes rather than a single fix.
Switch to an SLS-Free Toothpaste
Sodium lauryl sulfate (SLS) is a foaming agent in most mainstream toothpastes, and it’s one of the most actionable triggers to eliminate. SLS can strip the protective lining of your mouth, making the tissue more vulnerable to breakdown. Some clinical reports have found up to a 70% reduction in ulcers after switching to SLS-free toothpaste, though results vary. A double-blind trial of 90 people with recurrent ulcers found the SLS-free group didn’t necessarily get fewer ulcers overall, but they reported less pain and slightly faster healing. That alone makes it worth trying, especially since SLS-free options are widely available and cost roughly the same.
Look at the ingredients list on your toothpaste. If “sodium lauryl sulfate” appears, swap it out for a brand that omits it. Give it at least six to eight weeks before judging whether it helps, since ulcer cycles can take time to shift.
Check for Nutritional Deficiencies
Low levels of vitamin B12, folate, and iron are well-established contributors to recurrent mouth ulcers. The NHS lists mouth ulcers alongside a sore, red tongue as a hallmark symptom of B12 or folate deficiency. Iron deficiency works through a similar mechanism, impairing the body’s ability to maintain healthy oral tissue.
If you get ulcers frequently and can’t pin them on an obvious trigger, a blood test from your GP can check these levels. Correcting a deficiency often reduces ulcer frequency noticeably. In the meantime, making sure your diet regularly includes leafy greens, eggs, meat or fish, and fortified cereals covers the most common gaps. Vegetarians and vegans are at higher risk for B12 deficiency specifically, since it’s found almost exclusively in animal products or supplements.
Reduce Mouth Injuries
Physical trauma is one of the most common and preventable triggers. Biting your cheek, brushing too aggressively, or catching your gum on a sharp chip can create the perfect entry point for an ulcer, especially if you’re already prone to them.
If you wear braces, orthodontic wax applied over sharp or protruding brackets creates an effective barrier between the metal and your cheeks. Silicone strips are a newer alternative that stick better and last longer than traditional wax. Modern bracket designs with rounded edges also help, so if you’re starting orthodontic treatment, it’s worth asking about self-ligating systems that reduce friction against the inner cheeks and lips.
Beyond braces, a softer-bristled toothbrush and gentler brushing technique can make a real difference. Hard-bristled brushes and vigorous scrubbing damage the delicate tissue inside your mouth, particularly along the gumline and inner lips where ulcers commonly form. Poorly fitting dentures or rough dental work are also worth addressing with your dentist if ulcers keep appearing in the same spot.
Manage Stress Before It Triggers an Outbreak
Stress is one of the major factors in recurrent mouth ulcers. When you’re under pressure, your body releases cortisol, the primary stress hormone. Research published in the Journal of Oral Medicine and Oral Surgery found that people with recurrent ulcers had significantly elevated salivary cortisol levels during active outbreaks compared to healthy controls. Cortisol disrupts immune function, altering T cells, B cells, and natural killer cells in ways that can initiate fresh ulcer episodes.
The classic example is students developing ulcers during exam periods. If you notice your ulcers follow a predictable pattern tied to deadlines, travel, sleep loss, or emotional strain, that pattern itself is useful information. You may not be able to eliminate stress, but you can build in buffers during high-pressure periods: prioritizing sleep, maintaining exercise, and using whatever relaxation techniques work for you. Even modest stress reduction can lower cortisol enough to break the cycle.
Identify Your Food Triggers
Chocolate, peanuts, and eggs are among the foods most commonly reported to worsen ulcer episodes. Spicy food, despite its reputation, doesn’t actually cause mouth ulcers. No research supports a direct link between spicy food and ulcer formation. However, acidic and spicy foods can irritate an ulcer that’s already forming, making it larger or more painful. This is why it feels like spicy food “caused” the ulcer when it really just aggravated tissue that was already compromised.
Keeping a simple food diary when ulcers appear can help you spot personal triggers. Write down what you ate in the 24 to 48 hours before each ulcer shows up. After a few episodes, patterns often emerge. Common culprits beyond the ones listed above include citrus fruits, tomatoes, coffee, and certain cheeses. Once you identify a trigger, you don’t necessarily need to avoid it permanently. Sometimes reducing the frequency or amount is enough to keep ulcers from recurring.
Rule Out Underlying Health Conditions
Frequent, severe mouth ulcers can be a sign of a systemic condition rather than a standalone problem. Celiac disease is one of the most important to consider. People with celiac disease have more frequent and more severe canker sore outbreaks than the general population, and following a gluten-free diet has been shown to decrease both the frequency and severity of these outbreaks. If you also experience bloating, fatigue, or digestive issues alongside your ulcers, celiac testing is a straightforward blood test worth requesting.
Crohn’s disease and other inflammatory bowel conditions can also produce oral ulcers as an early or accompanying symptom. Behçet’s disease, a less common inflammatory condition, causes recurrent ulcers in the mouth and sometimes the genitals. Immune-suppressing conditions and certain medications (particularly those used in chemotherapy) are other known causes. If your ulcers are persistent, unusually large, or don’t respond to the prevention strategies above, the ulcers may be a symptom rather than the problem itself.
Use a Chlorhexidine Rinse During Flare-Ups
A chlorhexidine mouthwash can help reduce how often ulcers recur when used regularly during periods when you’re most vulnerable. It works by lowering the bacterial load in your mouth, which gives damaged tissue a better chance to heal before an ulcer fully develops. It’s not a primary treatment for active ulcers, but it serves as a useful preventive tool, particularly if you’re heading into a known high-risk period like a stressful stretch at work or after dental procedures.
Chlorhexidine rinses are available over the counter in most countries. Be aware that extended use can cause temporary tooth staining and altered taste, so it’s best used in targeted stretches rather than indefinitely.
When Ulcers Need Medical Attention
Most mouth ulcers heal on their own within one to two weeks. But certain patterns warrant a visit to your doctor or dentist. Cleveland Clinic flags these specific warning signs: ulcers lasting three weeks or longer, new sores appearing before old ones have healed, ulcers on the outer part of your lips (rather than inside the mouth), unusually large ulcers, painless ulcers, or ulcers accompanied by fever or diarrhea. A mouth ulcer that won’t heal is occasionally an early sign of oral cancer, particularly when it appears on or under the tongue. Most ulcers are harmless, but a non-healing sore is always worth having examined.