Patient information from BMJ

Canker sores

Last published:Apr 08, 2025

Canker sores are small sores inside the mouth. They are common and can be painful, especially if you keep getting them. But there are treatments that might help your canker sores heal more quickly and hurt less.

What are canker sores?

Canker sores are small, grayish-white sores inside your mouth. It's possible to get more than one at a time. They happen when the top layer of the skin is damaged. They often appear on the cheeks, the lips, and on the tongue. The sore is usually red around the rim.

In some people, canker sores can be bigger and take longer to heal. Often, these larger sores may leave scars.

Many people will get canker sores at some point in life. But it’s more common in teenagers and young adults. You may find you get them less often as you get older.

Usually, canker sores clear up on their own within a week. But some people might keep getting these sores every few weeks or months.

You might be more likely to keep getting canker sores if:

• they run in your family

• you are a nonsmoker or you’ve stopped smoking

• you have too little iron, folic acid, or vitamin B-12 in your blood

• you frequently injure the inside of your mouth (for example, from sharp or broken teeth, biting during chewing, or braces)

• you’re younger than age 30.

Some people seem to get sores after eating or drinking certain things: for example, chocolate, coffee, and peanuts. They may also be linked to stress or hormone imbalances during the menstrual cycle.

What are the symptoms of canker sores?

Canker sores can be very sore and uncomfortable, especially if you keep getting them. Eating or talking might make the pain worse. But apart from pain and discomfort, you shouldn’t have any other symptoms.

In a small number of people, canker sores can be a sign of other conditions such as:

• HIV infection

• inflammatory bowel disease (this refers to a group of serious conditions that affect the digestive system)

• celiac disease (a condition that makes you more sensitive to gluten).

This might be the case if you have symptoms like fever, weight loss, or sores on other parts of the body. It’s important to tell your doctor about any symptoms you have. This is so they can give you the right diagnosis.

What are the treatment options for canker sores?

There are few things you can do to help canker sores heal faster and reduce pain:

• switching to a toothpaste that does not contain sodium lauryl sulfate (SLS)

• avoiding foods and drinks you know will trigger your canker sores

• avoiding acidic foods and drinks, which can irritate the sore

• avoiding sharp food, such as crisps, which can scratch your mouth

• using a softer toothbrush.

Medicines to apply to your mouth

If you keep getting canker sores, your pharmacist, dentist, or doctor may recommend some medicines to help with your symptoms. For example:

• lidocaine mouthwash. This helps to numb your mouth and reduce your pain.

• chlorhexidine mouthwash. This is an antiseptic that reduces the chance of infections happening in your mouth. It also helps sores heal faster. 

Some people may struggle with chlorhexidine. This is because of its taste and the fact it makes some people feel sick.

Chlorhexidine can also sometimes cause mild pain in the mouth on rinsing. So your doctor might suggest diluting it (i.e., mixing it with water) first.

Regular use of chlorhexidine can lead to temporary teeth staining. To prevent this, you should thoroughly brush your teeth (or dentures) before using this medicine. This staining should go away when you stop using chlorhexidine.

If these medicines don’t help enough, your doctor or dentist might suggest using corticosteroids (also known as steroids). These are anti-inflammatory medicines that come as a paste, or as a tablet that dissolves in your mouth or in water.

Side effects of these steroids are rare. But occasionally, they may cause a mouth infection called thrush.

Vitamin B12 supplements

Vitamin B12 supplements may help, even in people who don’t have low levels of vitamin B12. So your doctor might recommend you take this medicine too.

What happens next?

Canker sores usually clear up on their own within a week. If you keep getting them, and the treatment your doctor prescribed doesn’t work, you may be referred to a specialist.

Canker sores aren’t usually a sign of anything serious. But if you have a single sore for more than 3 weeks, then speak to your doctor or dentist. They will want to rule out anything serious, like mouth cancer.

You should also let your doctor know if you have any other symptoms like fever, weight loss, or sores elsewhere on the body. This is so they can rule out other conditions, like HIV infection or inflammatory bowel disease.