Oral Health
Why do I keep getting canker sores in my mouth?
17 September 2026 · The Dentist, Al Qusais, Dubai
The short answer
Most recurrent canker sores (aphthous ulcers) come from a combination of minor mouth trauma, stress, acidic or spicy foods, and sometimes a shortfall in iron, B12 or folate. A sharp tooth edge, rough filling or badly fitting denture can also keep triggering the same spot. If you're getting them more than four or five times a year, if one lasts longer than two weeks, or if they come in clusters, it's worth having a dentist look at your mouth and possibly suggest a blood test.
What's usually behind them
Canker sores, properly called aphthous ulcers, are not caused by a virus like cold sores are. They're small breaks in the lining of the mouth, usually on the inside of the cheek, the lips or the base of the gums, and they tend to follow a pattern once you look closely. The most common trigger is simple mechanical damage: biting your cheek while chewing, a toothbrush bristle catching the gum, or a sharp edge on a tooth or old filling rubbing the same spot every day.
Stress and lack of sleep are genuinely linked to outbreaks, though nobody fully understands the mechanism. Acidic foods (citrus, tomato, vinegar) and very spicy food can irritate the tissue enough to set one off if you're already prone to them. Some people react to sodium lauryl sulphate, the foaming agent in most toothpastes, and switching to an SLS-free formula stops the sores completely for them. Hormonal shifts, particularly around the menstrual cycle, are another common trigger that patients often don't connect to their mouth.
When it's a nutrient gap or something needing a closer look
If sores are showing up regularly rather than once or twice a year, it's worth thinking about diet. Low iron, vitamin B12 or folate are well established causes of recurrent aphthous ulcers, and the fix can be as simple as a supplement once a blood test confirms the gap. This is genuinely worth raising with your GP if you're vegetarian, have heavy periods, or have any digestive condition that affects absorption, such as coeliac disease or Crohn's, both of which can show up first as mouth ulcers before any gut symptoms appear.
In the dental chair, what I'm checking for is anything physically causing repeated trauma: a cracked filling, a wisdom tooth pushing at an angle, a denture clasp that's stopped fitting properly, or braces wire poking into the cheek. Fixing that source usually stops the sores appearing in that exact location, even if the underlying tendency to get ulcers elsewhere doesn't fully go away. I'd also want to rule out anything unusual if a sore doesn't heal within two to three weeks, since most aphthous ulcers resolve well within that window and anything that lingers longer deserves a proper look rather than an assumption.
What actually helps, and when to book a check
Day to day, a saltwater rinse a few times a day, avoiding sharp or acidic foods while it heals, and an over-the-counter gel containing benzydamine or a protective paste can take the edge off pain considerably. Most single sores heal in seven to ten days without any treatment at all. What's not normal is a mouth that produces new ulcers every few weeks, or ulcers that are unusually large, deep or numerous, since that pattern points to either a mechanical cause in the mouth or something systemic worth investigating.
If that's your pattern, the honest next step is to have a dentist examine your teeth, fillings and any dental appliances for rough edges, and to have a chat about whether a blood test makes sense. At The Dentist in Al Qusais, the first checkup for new patients is free, so there's no cost barrier to finding out whether something fixable in your mouth is behind the recurring sores. You can book online at thedentist.ae/book or message on WhatsApp, and we're open every day except Sunday.
This article is general information, not a diagnosis. If you are in Dubai, the free first checkup at our Al Qusais clinic is the fastest way to get an answer about your own teeth.