What Are Canker Sores? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Canker sores are small shallow ulcers that form in the mouth. They’re not contagious, and in most cases they will heal on their own or with the help of at-home remedies. While they can be irritating and painful, they’re usually nothing to worry about. Sometimes, though, these sores can be a sign of a more serious underlying disorder. Whether you’re dealing with your first canker sore or you have a long-standing history with these lesions, here’s what you need to know about mouth ulcers.

Most canker sores are minor, measuring about 1 millimeter in diameter. (1) These white or yellowish spots, also known as aphthous ulcers, are oval or round, and sometimes have a red border. (2)

While the location of a sore can vary, you’ll typically find canker sores in the soft tissue of the mouth: underneath the tongue, at the base of the gums, or inside the cheeks or lips.

Mild pain is typical with a minor sore, whereas major sores can be extremely painful. (1,2)

Learn More About the Symptoms and Diagnosis of Canker Sores

The exact cause of a canker sore is unknown, but there are several situations that make them more likely to appear, says Samantha Rawdin, DMD, a prosthodontist based in New York City.

Common triggers include these events: (1,2,3)

• Oral injury during a dental procedure or from brushing too hard, playing sports, or biting your cheek while chewing
• Sensitivity to sodium lauryl sulfate (an ingredient in some mouthwashes and toothpastes)
• Hormonal changes during menstruation
• Nutritional deficiencies
• Emotional stress
• Food allergies
• Family history of canker sores
• Personal history of a chronic disease (celiac disease, Crohn’s disease, ulcerative colitis, or a condition that weakens the immune system)

Learn More About the Causes and Risk Factors of Canker Sores

There isn’t a specific test to diagnose a canker sore. (4) Rather, your doctor or dentist can make a diagnosis with a visual examination. If a sore is suspicious or doesn’t look like a canker sore, your doctor may recommend a biopsy to identify the lesion. This procedure removes a tissue sample from the lesion for further examination. (5)

Prognosis of Canker Sores

The good news is that most canker sores go away in one to two weeks without treatment.

You don’t have to see a doctor for a canker sore. But this doesn’t mean that you should ignore a sore. Keep an eye on the lesion and talk with your doctor or dentist if your condition worsens or doesn’t improve.

As a general rule of thumb, see your primary care doctor or a dentist if a canker sore increases in size or lasts longer than two weeks. You should also see a doctor if you have extreme pain or if a fever accompanies a canker sore. Sluggishness and swollen lymph nodes accompanying a sore are cause for consulting your doctor. (1,2)

If you don’t have a prior history of canker sores, you may be wondering: Are canker sores and cold sores the same thing?

Both canker sores and cold sores (fever blisters) cause oral lesions, but these conditions are quite different, says Dr. Rawdin.

“Recurrent canker sores differ from cold sores, which are caused by the herpesvirus, in that they are not contagious and they won’t form on the keratinized tissues of the oral area, such as the lips and along the gumline of the teeth,” explains Rawdin. Cold sores, on the other hand, are extremely contagious, and spread through saliva or skin contact. (1)

Keep in mind that not every sore in the mouth is a canker sore. See your doctor or dentist if you can’t distinguish a canker sore from a cold sore or if you feel you might have another type of sore.

Oral lesions that could mimic canker sores include these conditions: (6,7,8)

• Leukoplakia These white spots in the mouth aren’t painful but could be precancerous.
• Lichen Planus This inflammatory condition can cause white spots in the mouth.
• Oral Thrush This is a fungal infection that produces white patches inside the mouth.
• Oral Cancer Painful small white ulcerations may be a sign of oral cancer.
• Erythroplakia These red or lesions, which tend to last longer than canker sores, can also be precancerous.

Some of the above lesions are harmless and cause only mild discomfort. Other lesions, however, especially precancerous ones, are more serious. It’s important to investigate any lesions that persist.

It’s possible that a lesion could be a sign of oral cancer. In such a scenario, early diagnosis and treatment may prevent the cancer from spreading to other parts of the body, including the esophagus and lymph nodes. When a suspicious spot appears, it’s also important to rule out erythroplakia and leukoplakia, which could be precancerous or cancerous. (9)

Learn More About Distinguishing Canker Sores From Other Lesions

Most canker sores are short-lived. They typically clear up in one to two weeks, although a major canker sore may take up to six weeks to heal. (2)

Minor sores heal without leaving a scar, and pain or stinging gradually improves after a couple of days.

Major canker sores are less common and tend to be larger and deeper than minor sores. Because of the depth, these sores are more painful and take longer to heal. There’s also the risk of scarring with a major canker sore. (2)

Herpetiform canker sores are a rare form of these lesions, consisting of clusters of tiny sores (anywhere from 10 to 100) or a single large lesion. Fortunately, these sores usually heal without scarring. Don’t let the name confuse you — herpetiform canker sores aren’t caused by the herpes simplex virus, nor are they contagious. (2)

You can expect complete healing in about one to two weeks for a minor or herpetiform canker sore. Major canker sores take longer to heal, about six weeks. (2)

Canker sores are also divided into two categories: simple and complex. Simple sores occur about three or four times a year. Complex sores develop more often and tend to last longer. (1)

For canker sores that cause pain, many over-the-counter products can relieve symptoms and promote healing.

Medication Options

Mouth rinses, topical pastes, or creams containing dexamethasone (Decadron) or lidocaine help reduce inflammation. (1,4)

Pain relievers like ibuprofen (Advil, Motrin) can alleviate inflammation.

If you have a stubborn canker sore that doesn’t respond to home treatment, talk to your doctor or dentist to see if a prescription cortisone gel or an antibacterial mouthwash is right for you. If sores are complex and extensive and don’t respond to topical treatment, your healthcare provider may prescribe an oral corticosteroid to speed healing. Prolonged use of systemic corticosteroids has adverse effects, though, so an alternate course of treatment is recommended for people with chronic sores. (4)

You may even be a candidate for cauterization, in which a laser or chemical treatment is used to sear the affected tissue. (4)

Alternative and Complementary Therapies

You can make your own mouth rinses using a solution of salt and warm water or hydrogen peroxide and water. Gargling with these (but not swallowing them) can help lessen irritation. Another home remedy you might try is an application of calming aloe vera gel.

You can apply a mixture of half hydrogen peroxide and half water directly to the sore using a cotton swab, and then dab a small amount of magnesium hydroxide (Milk of Magnesia) on the sore. Repeat this three to four times a day. (3)

You might also try sucking on ice chips to numb the area.

Learn More About Treatment for Canker Sores: Medication, Alternative and Complementary Therapies, and More

Prevention of Canker Sores

Since the cause of canker sores is unknown, you may not be able to prevent all outbreaks. But a few adjustments to your daily routine may reduce your number of outbreaks.

Acidic foods and drinks can cause canker sores in some people, so avoid any foods that irritate your mouth. “If my patients complain about regular canker sores, I recommend keeping a food diary,” says Jennifer Silver, DDS, a dentist based in Calgary, Alberta.

“Write down everything you eat and drink, as well as whenever you get a canker sore. You may start to notice that consuming certain foods or drinks will correlate with a canker sore outbreak,” Dr. Silver says. These foods might include pineapple, tomatoes, grapefruit, and oranges, and spicy or salty foods.

There’s also a connection between canker sores and nutritional deficiencies. (1)

“Optimizing nutrition is the first defense against recurrent canker sores,” explains Deborah Malkoff-Cohen, RD, a dietitian based in New York City. Deficiencies that can contribute to canker sores include vitamin B12, iron, zinc, and folic acid. Eating a well-balanced diet or adequate supplementation is how you keep your immune system healthy and functioning at its best, notes Malkoff-Cohen.

Improving your oral hygiene may also lower the risk for canker sores. Be gentle when brushing your teeth to avoid injuring or irritating the delicate skin inside your mouth. And make sure you brush and floss every day to keep your mouth clean and eliminate bacteria. (10)

As an added precaution, stay away from oral products that contain sodium lauryl sulfate, in case you have a sensitivity to this ingredient. Sodium lauryl sulfate is found in some toothpastes and mouthwashes, so check the labels carefully, especially if you have recurring canker sores. (11)

About 20 percent of us regularly get canker sores. Though a canker sore can develop in anyone, sores tend to affect women more often than men. They occur more frequently in your teenage and young adult years, and it’s often around that age that people first develop canker sores. (1,2)

As noted above, canker sores sometimes result from nutritional deficiencies, such as too little vitamin B12, zinc, folic acid, or iron. (1)

And complex canker sores can occur in patients who have immune system diseases, such as lupus; inflammatory bowel diseases (Crohn’s disease, ulcerative colitis); and HIV/AIDS.

Mayo Clinic

For a comprehensive review of the symptoms, causes, diagnosis, and treatment of any number of health conditions, the Mayo Clinic is one of our favorite go-to resources. Their page on canker sores is no exception.

KidsHealth

Does your child get canker sores? Do you need help explaining what canker sores are and what to do about them? KidsHealth, from Nemours, has you and your child covered, with clear, easy-to-understand details on the topic.

MouthHealthy

MouthHealthy, from the American Dental Association, offers a ton of information on oral health and hygiene. And if you’re looking for a dentist, you can search on the site for one in your area.