9 Frequently Asked Questions About Canker Sores

Canker sores are typically minor — albeit annoying — lesions that form in the mouth. They can affect anyone, and many people will have at least one in their lifetime.

1. What Is a Canker Sore?

A canker sore, also known as an aphthous ulcer, is a small lesion — usually less than 1 millimeter, though it can be larger — that develops along soft tissue in the mouth, inside the cheek, along the gum line, or on the palate. (1) Canker sores don’t normally occur on the outer surface of the lips. (2)

Lesions can range from minor to major. Minor lesions are small and may only cause slight discomfort. With a major lesion, pain is more severe, with sores becoming larger and deeper. Fortunately, major canker sores aren’t as common. (2)

In rare cases, some people develop what’s called a herpetiform canker sore, which tends to be larger in size and more painful. This type of canker sore can appear as a single large, painful sore, or as clusters of sores inside the mouth. Despite their name, these lesions aren’t caused by the herpesvirus (which is responsible for cold sores or fever blisters). (2)

2. What Does a Canker Sore Look Like?

Canker sores are usually small, round or oval lesions. The center of a canker sore can appear white or yellow. Some people develop a red edge around their sores. (3)

3. What Causes Canker Sores and How Do You Get Them?

The exact cause of a canker sore is unknown. Yet certain factors can increase your risk of developing one sore or recurrent sores. (3)

A canker sore can form after injury to the mouth. An instrument may cut the delicate skin inside of your mouth during a dental appointment, or you may bite the inside of your mouth or lip while eating or playing sports. (1,2,3)

Mouthwashes and toothpastes containing sodium lauryl sulfate can also contribute to recurrent canker sores in some people who are sensitive to this ingredient. Avoiding these products may reduce the frequency of outbreaks. (2)

Acidic and spicy foods are known canker sore triggers in some people. Other possible triggers can include food allergies, Celiac disease, gluten intolerance, or a nutritional deficiency — such as a lack of vitamin B12, folic acid, zinc, or iron.

Stress and hormonal fluctuations can trigger canker sores, and there’s also a risk if you have a family history. (1,2)

If you have recurrent canker sores, see your dentist or primary care doctor to determine the underlying cause, says Samantha Rawdin, DMD, a prosthodontist based in New York City.

4. How Can I Get Rid of Canker Sores?

Canker sores are treatable at home and may not require checking in with your doctor or dentist. Gargling and rinsing the mouth with salt water, hydrogen peroxide, or a baking soda solution can help. These remedies can soothe inflammation, neutralize acid in the mouth, and remove bacteria, which all promote healing. (4,5)

The area around the sore is sensitive, so be careful when eating, brushing, and flossing. Even just tickling the spot with your tongue can irritate it and make it worse, says Jennifer Silver, DDS, a dentist based in Calgary, Alberta.

She further notes the importance of staying away from acidic or spicy foods, which may exacerbate an existing sore.

Pain is also common with a canker sore. To relieve tenderness, options include taking ibuprofen (Advil), sucking on ice, or applying aloe vera or oral numbing creams directly to the sore.  For oral numbing topical products, look for those with active ingredients such as benzocaine (Anbesol, Kank-A, Orabase, Zilactin-B), fluocinonide (Lidex, Vanos), or hydrogen peroxide (Orajel Antiseptic Mouth Sore Rinse, Peroxyl). (4)

5. Are Canker Sores Contagious?

Canker sores aren’t contagious; it’s not possible to give a canker sore to someone through kissing or sharing food and drinks. (3)

Even so, two people living in the same household may develop a canker sore at the same time if they eat the same trigger foods, or if they have similar allergies or intolerances to foods that cause sores.

6. Are Canker Sores Herpes?

The herpesvirus can cause cold sores (fever blisters), but these aren’t the same as a canker sore. (2)

The difference is that cold sores are contagious, so the virus responsible for them can pass from person to person through physical contact. Also, recurrent cold sores form outside of the mouth while canker sores form inside of the mouth. (2)

7. How Long Do Canker Sores Last?

Canker sores generally don’t last long, with most sores clearing on their own in about one week, explains Dr. Rawdin. It might take longer for a major or severe canker sore to heal — up to six weeks. (2)

Sores typically heal without scarring, although scarring is possible with a major lesion. (2)

8. What if My Canker Sore Isn’t Going Away?

Some canker sores don’t respond to home remedies and over-the-counter products. If a sore worsens or doesn’t improve, see your primary care doctor. Some deeper or larger lesions may need a prescription oral steroid medication like dexamethasone (Decadron) or a medicated mouthwash. (3,4)

Depending on the severity and duration of a canker sore, your doctor may suggest a cautery procedure. (4) This involves burning or destroying the tissue around the sore to promote healing. This might be an option for canker sores that cause severe pain.

9. How Do You Prevent a Canker Sore?

There’s no way to prevent canker sores, but modifying your diet might reduce the number of occurrences. (3)

For example, if you have a vitamin B12 deficiency, supplement with a multivitamin and eat a balanced diet. Consume plenty of fruits and vegetables, as well as lean meats and whole grains.

If you’re prone to canker sores, Dr. Silver suggests keeping a food diary and tracking what you eat and drink. “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 outbreak,” she continues.

You can also discuss allergy testing with your doctor to identify a food intolerance.

Protecting your mouth is another way to prevent lesions. Practice good oral hygiene — brushing your teeth twice a day and flossing once a day. But be gentle to avoid irritating the skin inside of your mouth. (2)

While canker sores are unpredictable, understanding their specific triggers might reduce the frequency of outbreaks and help speed the healing process.