Canker sores come back for most people because of a handful of repeating triggers, and stopping them means identifying which triggers apply to you. The most common culprits are mouth injuries from braces or biting your cheek, nutritional gaps, stress, and certain irritating foods or oral care products. Addressing even one or two of these can dramatically cut how often sores appear.
Fix Nutritional Gaps First
Deficiencies in vitamin B12, iron, and folate are well-established risk factors for recurrent canker sores. Your body needs these nutrients to maintain healthy oral tissue, and when levels drop, the lining of your mouth becomes more vulnerable to breakdown. A simple blood test from your doctor can check all three.
A notable clinical trial tested daily sublingual B12 (1,000 mcg) for reducing canker sore recurrence and found benefits regardless of whether participants had low B12 blood levels to begin with. That’s worth knowing: even if your B12 isn’t technically “deficient” by lab standards, supplementation may still help. B12 is water-soluble and difficult to overdose on, making it a low-risk option to try. Iron and folate, on the other hand, should be checked with bloodwork before supplementing, since excess iron carries its own health risks.
If you eat limited amounts of meat, leafy greens, or fortified cereals, these deficiencies become more likely. A daily multivitamin covering B12, folate, and iron can serve as a reasonable baseline while you sort out whether diet alone is enough.
Reduce Mouth Injuries
Physical trauma to the inside of your mouth is one of the most reliable canker sore triggers. This includes accidentally biting your cheek or tongue, irritation from braces or retainers, aggressive tooth brushing, and sharp edges on dental work like crowns or fillings.
If you wear braces, orthodontic wax is one of the simplest preventive tools available. Roll a small piece into a ball and press it onto any bracket or wire that rubs against your cheek, lip, or tongue. This is especially important in the first weeks after an adjustment, before your oral tissues have toughened up. A broken wire or loose band can cause sores quickly if left unprotected.
Switching to a soft-bristled toothbrush also helps. Stiff bristles can scrape the delicate tissue inside your mouth, creating tiny wounds that develop into full sores. Brush gently, and be especially careful around areas where you’ve had sores before.
Check Your Toothpaste
Sodium lauryl sulfate (SLS) is a foaming agent found in most toothpastes, and it’s a known irritant for people prone to canker sores. SLS strips away the protective mucus layer inside your mouth, leaving tissue more exposed to damage. Several studies have found that switching to an SLS-free toothpaste reduces canker sore frequency in recurrent sufferers. Brands like Sensodyne, Biotene, and some versions of Tom’s of Maine are SLS-free. This is one of the easiest changes you can make, and many people notice a difference within a few weeks.
Manage Chronic Stress
Stress is more than a vague “trigger” for canker sores. It works through a specific biological chain. When you’re under chronic stress, your body pumps out cortisol, which initially suppresses immune activity. Over time, though, your immune system becomes resistant to cortisol’s calming signals, and inflammatory molecules like TNF-alpha ramp up. These molecules attract immune cells that begin attacking the cells lining your mouth, causing the tissue breakdown that becomes a canker sore.
This explains why sores tend to cluster around exams, work deadlines, major life changes, or periods of poor sleep. The inflammation builds over days before you notice the sore itself. Reducing stress won’t eliminate canker sores on its own if other triggers are also at play, but for many people it’s the missing piece. Regular sleep, physical activity, and whatever stress-reduction practices actually work for you (meditation, time outdoors, breathing exercises) lower the baseline inflammatory load that makes sores more likely.
Be Strategic About Food
There’s no strong evidence that specific foods cause canker sores in the way an allergen causes a rash. Spicy food, for instance, doesn’t appear to trigger new sores. But acidic and abrasive foods can irritate tissue that’s already vulnerable or slightly damaged, making it more likely that a small wound progresses into a full sore.
The most commonly reported irritants include citrus fruits, tomatoes, vinegar-based foods, pineapple, and crunchy items like chips or hard toast that scratch the inside of your mouth. If you notice sores appearing a day or two after eating specific foods, try cutting them out for a few weeks and see if frequency drops. Keep in mind that the link is individual. Some people eat oranges daily with no issues, while others find them a reliable trigger.
Rule Out Underlying Conditions
If you’re getting canker sores more than three or four times a year despite addressing the triggers above, there may be something systemic going on. Celiac disease, inflammatory bowel conditions like Crohn’s disease, and immune disorders can all cause recurrent oral ulcers. Hormonal fluctuations, particularly around menstrual cycles, are another recognized pattern.
Food sensitivities that don’t rise to the level of a true allergy can also play a role. Some people find that gluten, dairy, or certain food additives correlate with outbreaks. An elimination diet, where you remove suspected triggers for two to four weeks and reintroduce them one at a time, is the most practical way to test this without expensive allergy panels.
A Practical Prevention Routine
Rather than trying everything at once, start with the changes most likely to make a difference:
- Switch toothpaste. Go SLS-free for at least a month and track whether sore frequency changes.
- Cover sharp hardware. Use orthodontic wax on braces, and ask your dentist to smooth any rough dental work.
- Supplement B12. A daily sublingual tablet of 1,000 mcg is the dose used in clinical research.
- Get bloodwork. Check iron, folate, and B12 levels, especially if you’re vegetarian or have heavy periods.
- Track your triggers. Keep a simple log of when sores appear alongside what you ate, your stress level, and any mouth injuries in the preceding days. Patterns usually emerge within two to three months.
Most people who get frequent canker sores have more than one contributing factor. Fixing just the toothpaste won’t help if you’re also B12-deficient and chronically stressed. But stacking a few targeted changes tends to produce a noticeable drop in how often sores show up, and in many cases stops them almost entirely.