What are canker sores?

Canker sores are small open ulcers that usually appear on the inside of your mouth. Causes include stress, hormonal changes, nutritional deficiencies, foods and other more. They usually heal on their own and don't require any treatment but can sometimes point toward an underlying issue.
Canker sores are small open ulcers that usually appear on the inside of your mouth. Causes include stress, hormonal changes, nutritional deficiencies, foods and more.

Canker sores (aphthous ulcers) are small open ulcers that show up in your mouth, typically inside the lip or cheek. They’re white or yellow in color and are often surrounded by red, inflamed tissue. 

These painful sores are among the most common oral conditions, and they affect almost half of all people. There are actually three main types of canker sore:

  • Minor aphthous stomatitis, which is the most common type, are small ulcers that heal within a week.
  • Major aphthous stomatitis, which is a more severe type, are larger and more painful. They heal within two weeks and often leave scars.
  • Herpetiform aphthous stomatitis, which occurs in less than 5% of people who have canker sores, is a cluster of tiny sores.

In many cases, canker sores heal on their own and don’t require any treatment. In some instances, however, they can point toward an underlying issue that may require medical treatment.

Signs and symptoms of canker sores

One of the most obvious signs of a canker sore is a small, painful yellow or white ulcer inside of your lip or cheek. For some, the sore appears on the gums. These sometimes get confused with cold sores. There are a few things that can help you to tell the difference.

One of the biggest differences between cold sores and canker sores is that cold sores appear on the outside of the mouth, usually around the lips. In some instances, they may show up on the roof of your mouth or tongue. Canker sores always appear inside the lips or cheeks. Another major difference between the two is that canker sores aren’t contagious, while cold sores are. 

Other signs and symptoms of canker sores include:

Tingling or burning inside your mouth

You may notice a tingling or burning feeling inside of your mouth before the canker sore appears. 


While it’s not always the case, some people develop a fever when they get a canker sore. A high fever can point toward a more serious issue.


Some people with canker sores may feel tired. 

Swollen lymph nodes

While not as common as some of the other symptoms, swollen lymph nodes may come along with a canker sore. The swelling may mean that there’s another issue going on, and you should schedule an appointment with your doctor. 

Causes of canker sores

Several different things can lead to a canker sore. Some of the most common include:


The connection between stress and canker sores isn’t well-understood, but studies do suggest that increased levels of stress can cause the ulcers to develop . 

Hormonal changes

Fluctuations in hormones may cause canker sores. Women who are prone to them may notice that the ulcers appear a few days before their period and go away after it’s done. 

Nutritional deficiencies

You might develop canker sores if your body is lacking certain nutrients. Some studies show that low levels of B vitamins can increase the risk of these painful ulcers. Other studies show that low iron levels may contribute to canker sores. 

Certain types of foods

Acidic foods, such as lemons, limes, oranges, tomatoes, strawberries, and more, can sometimes cause a canker sore to develop. You may also develop canker sores if you are sensitive to certain types of foods, such as chocolate, coffee, eggs, or anything spicy. 

Certain ingredients in toothpaste

Sodium lauryl sulfate, a common ingredient in toothpaste and mouthwash, can cause canker sores. Studies show people who use oral care products with this ingredient are more likely to have them.

Mouth injuries

Injuries to the soft tissues inside of your mouth — such as brushing too hard, biting your cheek, rubbing from braces, or ill-fitting dentures — can sometimes cause a canker sore to form. 

Autoimmune diseases

Canker sores may develop as a side effect of an autoimmune disease. The ulcers are linked to many conditions, such as:

Diagnosing canker sores

You don’t need to undergo any tests to diagnose a canker sore. Your doctor or dentist can identify them by looking at them. If your doctor believes that the ulcers are occurring as a result of an underlying condition, however, you may undergo other tests to determine what that issue is.

Treatments for canker sores

In many cases, canker sores go away on their own without treatment. Large or painful canker sores that last longer than two weeks, however, may need medical care. Some common treatment options for these ulcers include:

  • Over-the-counter or prescription topical medications, such as benzocaine or fluocinonide
  • Prescription mouthwashes 
  • Oral medications
  • Nutritional supplements
  • Cauterization of the sore

If your canker sores are the result of an underlying health condition, your doctor will provide recommendations to treat that issue. 


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Are cold sores and canker sores the same thing?

Although cold sores and canker sores have similarities, they are entirely different conditions.

Canker sores are not contagious, but cold sores are. Canker sores show up inside the mouth, while cold sores are often seen on the lips.

Cold sores

  • Cold sores are infectious.
  • It is also known as a fever blister or recurrent herpes labialis.
  • Cold sores are caused by a virus called HSV-1.
  • They are contagious and extremely painful for the first few days. First-time outbreaks may usually involve other symptoms, such as headacheswollen lymph nodes, muscle aches and a sore throat.
  • These sores are typically seen as a cluster of small blisters that quickly rupture to form small ulcers. The ulcerations may later extend to the skin around the mouth and become covered with a crust or scab.
  • Usually, cold sores appear outside the mouth, under the nose, around the lips or under the chin.
  • Lesions are commonly preceded by itching, burning and/or tingling sensations.
  • Cold sores usually are triggered by fever, emotional or physical stress, hormonal changes and/or decreased functioning of the immune system. They can be passed on to another person through kissing and sharing things that go in or near your mouth (like spoons or lipstick).
  • They generally heal within 7 to 10 days with or without treatment.
  • Applying petroleum jelly or aloe vera extracts or ice on the sores may numb the pain and speed up the healing process. In recurrent cases, doctors may prescribe antiviral drugs and creams, such as Valacyclovir.
  • To prevent a recurrence, individuals may need to maintain a hygienic lifestyle. Eating foods enriched with vitamin E and C may help in boosting the immune system.

Canker sores 

  • These sores are not usually infectious and are rarely contagious.
  • Canker sores are small round ulcers that appear inside the mouth usually on the inside of the cheek or near the gums. Canker sores are an autoimmune response of the body that damages the skin inside the mouth after a local injury.
  • They might be triggered by poor diet, local injury, food allergies, spicy food and vitamin deficiencies. Rarely, a virus may cause canker sores.
  • They often have a gray punched-out center and a white or yellow edge surrounded by redness. The sores bleed easily, usually when brushing the teeth.
  • They usually last for several days. Occasionally, they may last for 1 to 2 weeks before disappearing.
  • Canker sores are usually healed within 14 days. They may be treated with over-the-counter medications, such as Tylenol and Ibuprofen. Anesthetic ointment or gel may be applied for a short period to numb the pain. Dabbing a bit of cortisone or milk of magnesia on the affected area to coat the ulcer may reduce the pain.
  • Gargling with warm salt water or a solution of baking soda and water can shorten the healing time and reduce pain as well. A high-quality antimicrobial oral rinse may also help in the healing process.
  • Avoiding highly acidic or spicy foods and eating a diet rich in vitamins and nutrients may prevent recurrence. A toothpaste devoid of Sodium Lauryl Sulfate is known to prevent the recurrence of canker sores.

Should I be worried about cold sores and canker sores?

To summarize, canker and cold sores have characteristics that distinguish them from one another. Both sores are nuisances more than anything and they are not a major threat to health, but they are quite bothersome. Finding out whether you have a canker sore or a cold sore is the first step towards finding an effective treatment. Some people also deal with recurrent cold sores and canker sores. For a recurrent cold sore, the doctor may give suppression therapy with a daily antiviral to reduce the frequency of outbreaks. You should also see a doctor for repeated canker sores. This can be a sign of an autoimmune disease or a vitamin deficiency. Both canker sores and cold sores are two different conditions that signal weakness in the immune system. Fortunately, the immune system can be boosted with a healthy diet and a hygienic lifestyle.


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Medically Reviewed on 4/7/2022
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WRVO Public Media