Even though most canker sores are harmless and go away on their own in about one to two weeks, these lesions can be painful and annoying. (1)
Whether you’re dealing with your first canker sore or you have a history of repeated sores, preventing future problems starts with understanding why these lesions occur in the first place.
While the exact cause of canker sores is unknown, many factors can increase the risk of these mouth ulcers. Here’s a look at possible known triggers.
Injuring Your Mouth Can Lead to a Canker Sore
The skin inside of your mouth is delicate and sensitive. And unfortunately, it doesn’t take much to damage this soft area.
It can occur from brushing or flossing your teeth too roughly. Or you might sustain an injury during dental work or while playing sports. (2,3)
Accidentally biting the inside of your mouth while chewing on food can also lead to canker sores.
Toothpaste and Mouthwashes Can Irritate Your Mouth
Toothpastes and mouthwashes help maintain oral health by removing plaque from your teeth and freshening your breath. But if your oral hygiene products contain sodium lauryl sulfate (SLS), you may develop a canker sore if you’re sensitive to this ingredient. (1)
A 2017 review noted that in a trial conducted among patients using SLS-free products and a control group, the SLS-free products didn’t reduce the occurrence of sores, but did positively affect the healing process. (4)
If you have a history of canker sores, check the ingredient label of your oral products. Choose toothpastes and mouthwashes that don’t contain this ingredient, and then monitor your condition for improvement.
Diet Can Play a Role in Canker Sore Development
Certain foods are known triggers. These include salty foods and spicy foods, as well as acidic drinks and foods, such as oranges, lemons, tomatoes, and pineapples. (2)
A low intake of certain vitamins and nutrients — folic acid, zinc, iron — may also bring about canker sores. (2)
Research suggests that supplemental intake of vitamin B12 can help reduce the incidence of mouth ulcers. In a 2009 study, 58 people with recurrent canker sores were given 1,000 micrograms (mcg) of vitamin B12 at bedtime for six months. (5) The study found that after supplementing with the vitamin, 74 percent of participants no longer had sores at the end of treatment.
The Bacteria That Causes Stomach Ulcers Can Affect Your Mouth
Helicobacter pylori is a bacteria that causes infections in the stomach. It’s also the same bacteria responsible for peptic ulcers, which are sores in the lining of the stomach and the upper part of the small intestines. Sometimes the bacteria can be found in the oral cavity, triggering canker sores in some people. (1)
Other Possible Triggers: Hormonal Shifts, Heredity, and Stress
The Foods to Eat and Avoid if You’re Going Gluten Free for Celiac Disease
You’re also at risk for canker sores if you have a gluten intolerance or a gluten allergy (Celiac disease), or other food allergies. (1) But it’s important to note that canker sores aren’t always caused by food, notes Jennifer Silver, DDS, a dentist based in Calgary, Alberta.
These types of lesions can also run in families. So if your mother or father are prone to canker sores, you may be, too. (1,2,3)
Additionally, emotional stress and hormonal shifts can be culprits, as well as autoimmune diseases or conditions that cause inflammation, such as Crohn’s disease, Behcet’s disease, and HIV or AIDS. (1,2)
What Doesn’t Cause Canker Sores
Canker sores aren’t contagious — you can’t get a sore from kissing someone, sharing food or drinks, or touching another person’s lesions. (3)
Cold sores produce oral lesions, too. But unlike a canker sore, cold sores are contagious, warns Samantha Rawdin, DMD, a prosthodontist based in New York City. Cold sores or fever blisters are caused by the herpes virus, which doesn’t cause canker sores. (1)
In addition, recurrent cold sores occur outside of the mouth and don’t form on the “keratinized” tissues of the oral area (lips and along the gum line) like canker sores, Dr. Rawdin adds.
How to Prevent a Canker Sore
Since the exact cause of canker sores is unknown, prevention isn’t always possible. But you can take steps to reduce the likelihood and frequency of these sores.
“Write down everything you eat and drink, as well as whenever you get a canker sore,” says Dr. Silver. “You may start to notice that eating certain foods or drinks, typically things with high acidity or lots of spice, will correlate with a canker sore.”
Also, if you have known food allergies or gluten intolerance, avoid eating these foods, too.
Vitamin supplementation may also reduce your risk if you have a deficiency. So talk to your doctor about blood testing to check your levels.
Make sure you eat a healthy, balanced diet to receive adequate nutrients and minerals each day. This includes fruits, vegetables, lean meats, and whole grains.
Some people develop canker sores while under emotional stress. If you believe stress is a trigger, here are tips to reduce your stress level, and possibly reduce the frequency of outbreaks: (1,3)
- Practice deep breathing exercises or meditation
- Get plenty of sleep
- Exercise regularly
- Find enjoyable activities
- Eat a healthy diet
- Build your social connections
- Get counseling
Reducing canker sores might also be a matter of improving oral hygiene or changing your oral habits. This includes gently brushing your teeth at least twice a day and flossing daily to remove germs and bacteria. It’s worth seeing if you notice a difference when you use oral products that don’t contain sodium lauryl sulfate. (1)
Also, don’t ignore repeated canker sores. “If it’s a constant problem, see your dentist or primary care doctor to determine if there’s an underlying cause,” says Rawdin.
If you’ve taken steps to limit incidents, yet your condition hasn’t improved, talk to your doctor. The underlying trigger might be something you haven’t considered, such as a food allergy, chronic inflammation, or an autoimmune disease.