Causes of canker sores

A wide range of factors may trigger mouth canker sores. The exact cause may often be unknown and thus may not always be avoided.

What are canker sores?

Canker sores are small and painful mouth sores. These are not cancerous and usually resolve without treatment.

These sores are the commonest cause of mouth ulcers. It has been estimated that somewhere between 20% and 60% of the population have had canker sores at one time or another.

Common triggers and causes of canker sores

Common triggers and causes of canker sores include (1-6):

  • Unknown causes – in substantial number of cases the cause of canker sores is not known.
  • A wound within the mouth. This could be due to inadvertent biting of the lips, insides of cheeks or tongue during chewing or injury due to sharp foods or dentures or even sharp edges of teeth.
  • Weak immune system usually triggers canker sores. Those with a weak immunity do not have the strength and means to fight against the bacterial infections within the mouth after minor injuries and this leads to canker sores.

Some diseases of the immunity like Behcet’s disease or Kawasaki’s disease also cause increased risk of canker sores in the mouth.

  • Hormonal fluctuations lead to a risk of canker sores. Women with premenstrual tension and during their menstrual periods when there are hormonal changes are more at risk of canker sores. The causes are unknown.
  • Those with certain food allergies are at risk of canker sores. Due to allergies they may develop sores within their mouths that turn and develop into canker sores.

Some foods like spicy preparations, chocolates citrus, acid foods (vinegar, pickles) and excessive salted nuts or potato chips may lead to tiny mucosal injuries. These cause canker sores.

  • Chemical injuries to the inside linings of the mouth may occur due to excessive tobacco use, smoking and alcoholism. This type of injury also results from injury of the mucosal lining due to taking excessively hot beverages or foods.
  • Canker sores may occur due to viral infections.
  • Recent dental work, aggressive brushing or cleaning of the teeth may lead to injuries and susceptibility to canker sores.
  • Emotional stress such as examinations, anxiety, depression and other emotional upheavals may lead to an increased risk of canker sores. Physical stress may also lead to an increased propensity for canker sores.
  • Some studies have indicated that lack of certain vitamins and minerals in the diet like Vitamin B 12, iron and folic acid may lead to canker sores.
  • Women are more likely to get canker sores than men
  • In some individuals the risk of canker sores are inherited. These sores however do not spread from person to person by contact.

Further Reading

Last Updated: May 27, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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