Canker sores:

• Are usually round or oval with a white or yellow center and a red border.
• Form inside the mouth on or under the tongue, inside the cheeks or lips, at the base of the gums, or on the soft palate.
• May cause a tingling or burning feeling a day or two before the sores appear.
• Are painful and may make it hard to eat and talk.
• Can occur alone or in groups.

There are three types of canker sores. These include minor, major and herpetiform (her-PET-ih-form) canker sores.

Minor canker sores

Minor canker sores are the most common. They:

• Are usually small.
• Are oval shaped with a red border.
• Heal in 1 to 2 weeks.
• Usually do not leave a scar.

Major canker sores

Major canker sores are less common. They:

• Are larger and deeper than minor canker sores.
• Are usually round with defined borders but may have edges that are not evenly shaped when large.
• Can be very painful.
• May take up to six weeks to heal.
• Can leave scars.

Herpetiform canker sores

Herpetiform canker sores are not common, and they are not caused by herpes virus infection. These canker sores:

• Usually develop later in life.
• Are very small — each one is about the size of the head of a pin.
• Often occur in clusters of 10 to 100 sores. They may join together to form one large sore.
• Have edges that are not even.
• Heal in 1 to 2 weeks.
• Don't leave a scar.

When to see a doctor

Talk with your healthcare professional or dentist if you have:

• Large mouth sores.
• Sores that don't go away or that keep coming back, such as new ones appearing before old ones heal.
• Sores that last two weeks or longer.
• Sores that spread onto the lips.
• Pain that you can't control.
• Trouble eating or drinking.
• High fever along with mouth sores.

The exact cause of canker sores isn't clear. Experts believe that several factors may play a role. Possible triggers for canker sores include:

• Food sensitivities or allergies, such as to chocolate, eggs, nuts, and spicy or acidic foods.
• Certain toothpastes and mouth rinses that have sodium lauryl sulfate, a foaming agent.
• An injury to your mouth from dental work, brushing too hard, biting your cheek or playing sports.
• Some medicines, including certain medicines used to treat heart conditions and osteoporosis and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve, Anaprox DS, others).
• Hormonal changes during menstruation.
• Emotional stress.

Canker sores also may occur because of certain medical conditions, such as:

• Celiac disease, which is an autoimmune condition where the immune system reacts to gluten, sometimes causing damage to the small intestine. Gluten is a protein found in foods that have wheat, barley or rye.
• Low levels of vitamin B-12, zinc, folate or iron in the body that can happen from not eating a balanced diet.
• Inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis.
• Behcet disease, which is a rare condition that causes blood vessel inflammation throughout the body and mouth sores.
• A change in the immune system that causes the body to attack healthy cells in the mouth instead of germs such as viruses and bacteria.
• HIV/AIDS, which is a condition that damages the immune system so that the body is less able to fight infection and disease.

Canker sores are not caused by a herpes virus infection.

Anyone can get canker sores. But they're more common in teens and young adults. They're also more common in women than in men.

Some people who get canker sores often have a family history of the condition. This may be passed down from parents to children. It also could be due to shared factors in the environment, such as certain foods or allergens.

You may be able to lessen how often canker sores occur. These tips may help:

• Stay away from foods that irritate your mouth. These may include nuts, certain spices, salty foods and acidic fruits, such as pineapple, grapefruit and oranges. Don't eat foods to which you're sensitive or allergic.
• Choose healthy foods. Eat a balanced diet. Include a variety of fruits, vegetables and whole grains.
• Follow good mouth care habits. Regular brushing after meals and flossing once a day can keep your mouth clean and free of foods that might trigger a sore. Use a soft toothbrush to keep from irritating your mouth. Don't use toothpastes and mouth rinses that have sodium lauryl sulfate.
• Protect your mouth. See your dentist if you have sharp tooth surfaces or dental appliances that seem to trigger the sores. Ask about orthodontic waxes to cover sharp edges. Try a mouthguard during sports activities.
• Lower your stress. If your canker sores seem to be linked to stress, practice ways to lower your stress, such as meditation and guided imagery.

Tests aren't needed to diagnose canker sores. Your healthcare professional or dentist can diagnose canker sores by talking with you about your symptoms and looking in your mouth. If your canker sores are severe, don't go away or happen often, or if you have other symptoms, you may need tests to check for other health conditions.

Treatment usually isn't needed for minor canker sores. These tend to heal on their own in 1 to 2 weeks. You may need treatment if sores are large, do not heal or are very painful. Treatment may include mouth rinses, topical products, oral medicine, cautery of the sores or nutritional supplements. Or treatment for related health conditions may be needed.

Mouth rinses

If you have several canker sores, your healthcare professional may prescribe a mouth rinse that has the steroid dexamethasone (dek-suh-METH-uh-sown). This can lessen pain and swelling. A rinse that has lidocaine, a numbing medicine, can lessen pain.

Topical products

Prescription products and products you can buy without a prescription may help ease pain and speed healing. These include pastes, creams, gels or liquids that you put on the canker sore as soon as it appears.

Common active ingredients in topical products include:

• Benzocaine (Anbesol, Kank-A, Zilactin-B).
• Fluocinonide (Vanos).
• Hydrogen peroxide (Orajel Antiseptic Mouth Sore Rinse, Peroxyl Mouth Sore Rinse).

There are many other topical products for canker sores, including those without active ingredients. Ask your healthcare professional or dentist for advice on which may work best for you.

Oral medicines

Oral medicines may be used when canker sores are severe or don't heal with topical treatments. These may include:

• Medicines not intended specifically for canker sore treatment. Examples include colchicine used to treat gout and the intestinal ulcer treatment sucralfate (Carafate), a coating agent.
• Oral steroid medicines when severe canker sores don't heal with other treatments. Because of the potential for serious side effects, they're usually not the first treatment choice.

Cautery of sores

During cautery, tissue is burned away to get rid of the canker sore. Chemical cautery uses a substance placed on the canker sore. Low-level laser therapy also is an option. Cautery is used for more-painful or more-severe canker sores, especially to lessen pain.

Nutritional supplements

If testing shows that you have low levels of important nutrients, such as folate, vitamin B-6, vitamin B-12, or zinc, your healthcare professional may suggest a nutritional supplement.

Related health conditions

If a medical condition is causing your canker sores, your healthcare professional can treat the health condition.

To help lessen pain and speed healing of canker sores, these tips may help:

• Rinse your mouth. Use a saltwater or a baking soda rinse several times a day. For a saltwater rinse, mix 1/2 teaspoon (2.5 milliliters) of table salt in 8 ounces (237 milliliters) of warm water. To make a baking soda rinse, mix 1 teaspoon (5 milliliters) of baking soda in 1/2 cup (118 milliliters) warm water.
• Put a small amount of milk of magnesia on your canker sore a few times a day.
• Stay away from foods that are rough, acidic or spicy. These can cause more irritation and pain.
• Allow ice chips to slowly dissolve over the canker sores.
• Brush your teeth gently. Use a soft toothbrush and a toothpaste without a foaming agent such as Biotene or Sensodyne Pronamel.

Your healthcare professional or dentist diagnoses a canker sore based on your symptoms, medical history and how the sore looks. Here's some information to help you get ready for your appointment.

Before your appointment make a list of:

• Your symptoms, including when they started and if they've changed or worsened over time.
• All medicines you're taking, including vitamins, herbs and other supplements, and the doses.
• Other health conditions you have, if any.
• Key personal information, including any recent changes or stress in your life.
• Questions to ask your healthcare professional or dentist.

Some basic questions to ask:

• Do I have a canker sore? If not, what else could it be?
• What factors may be causing the sore?
• Do I need any tests?
• What treatment do you recommend, if any?
• What can I do to lessen pain? Is there anything I can do to speed up healing?
• How soon do you think my symptoms will get better?
• Is there anything I can do to keep from having another canker sore?

Feel free to ask other questions during your appointment.

What to expect from your healthcare professional or dentist

You may be asked:

• What are your symptoms?
• When did you first notice these symptoms?
• How severe is your pain?
• Have you had sores like this in the past? If so, have you noticed if anything seems to trigger them?
• Have you been treated for sores like this in the past? If so, what treatment worked best?

You also may be asked about possible triggers:

• Have you had any recent dental work?
• Have you recently had a lot of stress or major life changes?
• What is your typical daily diet?
• Have you been diagnosed with any other medical conditions?
• What medicines do you take?
• Do other family members also have canker sores?

Be ready to answer questions so that you'll have time to talk about what's most important to you.