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Updated on June 15, 2023
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Canker Sore Causes

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What Are Canker Sores & Where Do They Form?

Canker sores are a common type of mouth ulcer. They are otherwise known as aphthous ulcers. Canker sores are painful, exposed sores in the mouth. They are often small and round. They are white or yellow and are surrounded by a bright red border. 

Canker Sores

Aphthous ulcers can develop on the inside of your cheek, under or on your tongue, on your lips, or in the back of your throat.

Canker sores are not the same as cold sores, otherwise known as fever blisters. Cold sores result from herpes simplex virus. They develop on the lips, gums and hard palate, and are contagious, which canker sores are not. A canker sore is not cancerous.

In most cases, canker sores go away by themselves. However, there are over-the-counter (OTC) creams, ointments, mouthwashes, and rinses available that can help clear them up and reduce any pain. Painful sores can be relieved with over-the-counter medicines like ibuprofen.

Some home remedies can also help. Try mixing warm water with salt to make a mouth rinse to gargle. The salt water mouth rinse can help reduce the inflammation and pain of canker sores.

Avoiding hot and spicy foods when you have a canker sore helps. It would help if you also stayed away from acidic foods like citrus fruits like lemons and oranges.

If you experience major canker sores that are painful or persistent, speak to your doctor or health care provider for medical advice.

What Causes Canker Sores? 

It’s still not known why some people develop canker sores, and others don’t. They are believed to be hereditary and are also influenced by many other factors. Canker sores can also link to problems with the body’s immune system.

Common causes of canker sores include:

  • A mouth injury from dental work or a sports accident
  • Biting the tongue or cheek
  • Cleaning the teeth and tongue too roughly with a toothbrush
  • Emotional stress
  • A lack of certain minerals and vitamins in the diet. For example, iron, folic acid, or vitamin B12
  • Family genetics
  • Hormonal changes that may affect the menstrual cycle
  • Toothpaste and mouth rinses that contain sodium lauryl sulfate
  • Food allergies or sensitivities. Particularly to chocolate, coffee, eggs, nuts, cheese, strawberries, and spicy/acidic foods
  • A weakened immune system
  • Poor oral health and hygiene 

Certain diseases can cause inflammations in the mouth that resemble canker sores. These medical conditions include chronic inflammatory bowel disease or Behçet's disease.

Canker Sores On and Under the Tongue

Mouth ulcers found on and under the tongue have many causes, including the ones listed above.

Common causes of canker sores on and under the tongue include:

  • Emotional stress
  • Minor injury to the tongue
  • Eating spicy and acidic foods
  • Food allergies or sensitivities 

Canker Sores on the Gums

Mouth sores on the gums can result from many causes. 

Common causes of canker sores on the gums include:

  • A minor injury to your mouth from dental work
  • Aggressive brushing of the teeth with a toothbrush
  • Sports accident
  • Using toothpaste and mouth rinses containing sodium lauryl sulfate 
  • Food sensitivities or intolerances 
  • Poor oral health and hygiene 

Canker Sores on the Lips

Common causes of canker sores on or inside of the lips include:

  • Injury or tissue damage due to dental work
  • Sports accident
  • Accidentally biting the lip
  • Using toothpaste and mouth rinses containing sodium lauryl sulfate 
  • Poor oral health and hygiene 
  • Eating spicy or acidic foods
  • Hormonal changes
  • Emotional stress
  • A weakened or overactive immune system

Canker Sores in the Throat

While mouth sores usually develop inside the mouth or on the lips, they can sometimes form in the back of the throat and the tonsils. 

Canker sores in the throat are often more challenging to treat. Applying a cream or gel directly onto mouth ulcers can be difficult. However, a medicated mouth rinse or wash can help clear up canker sores in the throat.

Mouth ulcers in the throat often result from something you ate or drank. This is because your tonsils come in contact with irritants when you swallow. A vitamin B12 deficiency can also lead to canker sores in the mouth and on the tonsils.

Common causes of canker sores in the throat include:

  • Eating acidic or spicy foods
  • Food sensitivities or intolerances 
  • A vitamin B deficiency

What Causes Frequent Canker Sores?

People experiencing recurrent canker sores often have a family history of the medical condition. This may be due to genetics or a shared factor in the environment, such as consuming certain foods or allergens.

Canker sores that persist may link to celiac disease, inflammatory bowel disease, or HIV/AIDS.

What Causes Canker Sores in Kids?

Children and teens often develop canker sores between the ages of ten and 19. Around three in ten children experience mouth ulcers. Canker sores cannot spread from one child to another.

Common causes of canker sores in kids include:

  • An injury or stretching of soft tissues in the mouth. This can occur during a dental procedure or teeth cleaning
  • Biting of the tongue or inside of the cheek
  • Infection and viruses
  • Eating certain foods
  • Emotional stress
  • A weakened or overactive immune system
  • Poor oral hygiene and health
  • Poor nutrition
  • Irritation from orthodontic braces
  • Certain medicines
Last updated on June 15, 2023
5 Sources Cited
Last updated on June 15, 2023
All NewMouth content is medically reviewed and fact-checked by a licensed dentist or orthodontist to ensure the information is factual, current, and relevant.

We have strict sourcing guidelines and only cite from current scientific research, such as scholarly articles, dentistry textbooks, government agencies, and medical journals. This also includes information provided by the American Dental Association (ADA), the American Association of Orthodontics (AAO), and the American Academy of Pediatrics (AAP).
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  3. Dalessandri, D., Zotti, F., Laffranchi, L. et al. Treatment of recurrent aphthous stomatitis (RAS; aphthae; canker sores) with a barrier forming mouth rinse or topical gel formulation containing hyaluronic acid: a retrospective clinical study. BMC Oral Health 19, 153, 2019,
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  5. Canker Sores (Aphthous Ulcers) in Children, University of Rochester Medical Center,
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